Digital Drawing on a Tablet: Flat Colors, Shading, and Simple Rendering with Layer Control

A tidy beginner coloring system (so you can render without chaos)

The goal of this chapter is a simple, repeatable structure: one set of flat colors that stays clean, plus one shadow layer and one highlight layer that you can adjust anytime. If your flats are solid and well-separated, everything else becomes easier: selections are faster, shading stays inside shapes, and edits don’t damage your base colors.

Recommended layer stack for clean rendering

• Line Art (top). Keep it visible while you color.
• Highlights (blend mode: Screen/Add). One layer to start.
• Shadows (blend mode: Multiply). One layer to start.
• Flats (base colors). This is your “map” of the drawing.
• Background (optional).

Keep names literal (Flats, Shadows, Highlights). Avoid making many “temporary” layers—tidy naming and a small stack is part of staying clean.

Flatting methods that stay tidy

Flatting means filling each major shape with a solid color (no gradients). The colors don’t need to be correct yet; they need to be separate and selectable. Choose one of these methods depending on your line art and your app’s tools.

Method A: Fill tool with threshold/tolerance (fastest when line art is closed)

Most fill tools have a threshold/tolerance setting. Low threshold fills only very similar pixels; high threshold floods more area (risking leaks).

1. Create a Flats layer under the line art.
2. Select the Fill tool and set it to fill on the active layer (not on all layers unless you intend it).
3. Adjust threshold/tolerance: start mid-range, then test on a small area.
4. Tap inside a shape to fill it.
5. If it leaves a thin unfilled rim near the line, increase threshold slightly or use a “expand fill/close gap” option if your app has it.

Tip: If your app offers “Close Gap” levels, use the smallest setting that prevents leaking. Over-closing can fill through intended openings (like hair strands or small holes).

Continue in our app.

• Listen to the audio with the screen off.
• Earn a certificate upon completion.
• Over 5000 courses for you to explore!

Or continue reading below...

Download the app

Method B: Selection-based fills (most reliable for tricky line art)

This method is slower but extremely clean. You define the shape first, then fill it.

1. On the Flats layer, use a selection tool to outline a shape (lasso/pen selection).
2. Fill the selection with a flat color (bucket fill inside selection or paint then fill).
3. Deselect and move to the next shape.

Why it’s tidy: You’re not trusting the line art to be perfectly closed; you’re explicitly defining the boundary.

Method C: Paint on clipped layers (clean edges without re-selecting)

If your flats are already in place, you can paint variations without repainting edges by using a clipped layer above the Flats.

1. Create a new layer above Flats.
2. Set it to Clip (or “Clipping Mask”) to the Flats.
3. Paint freely—your strokes stay inside the flat shapes.

Use case: Great for subtle color shifts, texture, or small corrections without damaging the base flats.

Fixing gaps and halos around line art

Common flatting problem: a thin “halo” of unfilled pixels between the flat color and the line art, especially if the line is anti-aliased (soft edges). Fix it early so shading doesn’t reveal messy edges.

Quick fixes (choose one)

• Expand the filled area: If your app has “Expand selection” or “Grow,” expand by 1–3 pixels before filling. This tucks flats under the line art.
• Fill tool options: Increase threshold slightly, or enable “Fill to reference layer” and “Area scaling/expand” if available.
• Manual edge pass: Use a hard brush on the Flats layer and trace just under the line art where halos appear. This is slow but precise for problem areas.

Spot-check routine (fast and effective)

1. Hide the line art briefly.
2. Zoom in and look for tiny white gaps between shapes.
3. Turn line art back on and fix only the gaps you can actually see at normal viewing size.

Don’t chase microscopic perfection—fix what will show in the final image.

A simple light model you can apply to anything

To keep rendering beginner-friendly, use a single light direction and two layers: one for shadows, one for highlights. This creates readable form without overcomplicating.

Step 1: Choose a light direction (and commit)

Pick one direction like “top-left” or “top-right.” Mentally label three zones on each form:

• Light side: faces the light.
• Shadow side: faces away from the light.
• Core shadow / occlusion: where light is blocked the most (under overlaps, inside folds, under the chin).

Keep it consistent across the whole drawing. Consistency reads as “skill” even with simple shading.

Step 2: Add one shadow layer (Multiply) with controlled opacity

1. Create a layer above Flats named Shadows.
2. Set blend mode to Multiply.
3. Clip it to Flats (so shadows stay inside shapes).
4. Choose one shadow color (a slightly cool or slightly warm darker tone). Avoid pure black.
5. Paint shadows on the side away from the light. Start with low opacity and build up.

Practical shadow placement checklist:

• Under overhangs (hair over forehead, hat brim, chin over neck).
• Inside creases (folds, corners of the mouth, between fingers).
• Where objects touch (arm against torso, collar against neck).

Step 3: Add one highlight layer (Screen/Add) with controlled opacity

1. Create a layer above Shadows named Highlights.
2. Set blend mode to Screen (softer) or Add (stronger). If Add looks too intense, switch to Screen.
3. Clip it to Flats.
4. Pick a highlight color (often a lighter, slightly warmer version of the local color, not pure white).
5. Paint highlights on planes facing the light: top edges, cheekbones, shoulder tops, glossy areas.

Control tip: Keep highlight opacity lower than you think at first. It’s easier to add intensity later than to fix blown-out highlights.

Keeping rendering clean (and avoiding the “muddy” look)

Limit brush variety to stay consistent

Use just two brushes for this chapter’s workflow:

• Hard round (or a hard-edged inking brush) for crisp edges and graphic shadows.
• Soft round (or airbrush) for gentle transitions when needed.

Too many textured brushes early on can make surfaces look noisy and inconsistent.

Keep edges intentional: hard vs soft

Decide what kind of edge each shadow needs:

• Hard edge (use hard brush): cast shadows, sharp folds, graphic style, clear separation.
• Soft edge (use soft brush): rounded forms, subtle transitions, soft materials.

A common beginner issue is making everything soft. That removes structure. Mix edges on purpose: mostly hard, with a few soft transitions where form actually turns.

Avoid muddy colors: sample, then adjust (don’t endlessly blend)

Mud happens when you repeatedly blend mid-tones until everything becomes grayish. Instead:

• Sample the local color from the Flats.
• Move it slightly darker/cooler for shadows or lighter/warmer for highlights.
• Lay it down cleanly on the Multiply/Screen layer with controlled opacity.

If your shadow looks dirty, it’s often because it’s too desaturated or too close to gray. Nudge saturation up a little, or shift hue slightly (cooler shadows, warmer lights is a simple starting rule).

Guided exercise: flats + one shadow layer + one highlight layer

Use a simple line art drawing (a character bust, a fruit bowl, or a small object with clear shapes). The goal is not realism—it’s a clean, editable render with minimal layers.

Exercise setup (2 minutes)

1. Prepare your layer stack: Line Art (top), Highlights, Shadows, Flats.
2. Decide light direction (example: top-left).
3. Pick a limited palette: 5–8 flat colors total.

Step 1: Create flats (10–25 minutes)

1. On the Flats layer, fill each major shape: skin, hair, shirt, eyes, accessories, etc.
2. Use one flat color per shape group (don’t over-segment).
3. Fix halos/gaps using expand fill or a quick manual edge pass.
4. Hide line art briefly to check that shapes are clean and fully filled.

Checkpoint: If you can tap-select or quickly isolate any major area (depending on your app), your flats are doing their job.

Step 2: Add one shadow layer (8–15 minutes)

1. Set Shadows to Multiply and clip it to Flats.
2. With a hard brush, block in the big shadow shapes first (shadow side of the form).
3. Add a few occlusion accents: under chin, under hair, between overlapping forms.
4. Use the soft brush only for one or two gentle transitions (like a cheek or round object).

Rule: If you’re unsure, keep shadows simpler and larger. Small, noisy shadows make the drawing look dirty.

Step 3: Add one highlight layer (5–10 minutes)

1. Set Highlights to Screen (or Add if you want punch) and clip it to Flats.
2. Place highlights only where the light hits most: top planes, edges, small specular spots.
3. Keep it restrained—highlights should guide the eye, not cover everything.

Step 4: Refine only key focal areas (10–20 minutes)

Choose 1–2 focal zones (example: face and hands; or the main object and its label area). Refine there only:

• Sharpen a few edges (hard brush) to increase clarity.
• Add one extra shadow shape to describe form (not many).
• Add one controlled highlight accent to emphasize material (glossy eye, shiny metal, etc.).

Leave non-focal areas simpler. This keeps the image readable and prevents over-rendering everywhere.

Self-check table (quick diagnostics)