How to Fill Colors on a Separate Layer Using Line Art as the Boundary in Krita

Arrange your layers from top to bottom as Line Art, Flat Colors, and an optional background. Krita draws higher layers over lower ones, which lets the outlines cover the edges of the color beneath them. However, an opaque white background inside the line-art layer will also cover those colors. Krita Manual: Flat Coloring

Before filling, check which kind of line art you have:

• Lines on transparency: Keep the line-art layer above your colors.
• Black lines on white: Set the line-art layer’s blending mode to Multiply for a straightforward coloring setup.
• White that needs actual transparency: Duplicate the original as a backup, then apply Filter → Colors → Color to Alpha to the working copy and remove white.

Multiply changes how the layer combines with the colors below; it does not remove the white pixels. Colored outlines can also alter the appearance of underlying colors in Multiply mode. Color to Alpha creates actual transparency and can work with colored outlines because it removes the specified background color. Choose the preparation method before judging your fills. Krita Manual: Flat Coloring

Use the new-layer button in the Layers docker to create a paint layer, then move it below the outlines and name it Flat Colors. Krita’s standard new-layer button creates a paint layer; Insert is also the documented shortcut. A paint layer holds the pixels you will add with the bucket and brush. Krita Manual: Paint Layers

Select Flat Colors before each filling session. Check that the layer is visible, editable, and at the intended opacity. You can reorder layers by dragging them in the Layers docker, and the same panel controls visibility and editing state. Locking the completed line-art layer is a useful precaution against accidentally drawing on it. Krita Manual: Layers

For your first pass, one color layer keeps the setup easy to inspect. If you later want separate layers for different character parts, create additional paint layers beneath the outlines and select the appropriate destination before filling each part.

Select the Fill Tool, then open its Tool Options docker. Tool options appear after you select the tool; if the panel is missing, look under Settings → Dockers. Francesco Milanese: Krita Fill Tool Basics, Krita Manual: Settings Menu

Use this starting setup:

1. Set Fill Mode to Contiguous Region.
2. Set Fill Source to Foreground Color, then choose your color.
3. Under Reference, choose All layers.
4. Keep Flat Colors selected and click inside one closed outline.

All layers samples the visible layer stack. Current Layer samples only the selected layer, so an empty destination layer supplies no outline boundary. Krita Manual: Fill Tool

Do not use Shift + Backspace as a substitute for the boundary-aware bucket. That shortcut fills the active selection uniformly; without a selection, it fills the entire layer. It is useful later when you deliberately create a selection first. Francesco Milanese: Krita Fill Tool Basics

After the first click, briefly hide Line Art. The colored shape should remain visible on Flat Colors. Restore the outlines, then briefly hide Flat Colors: the original drawing should remain. This simple inspection confirms that the color and outlines are separate before you repeat the operation across the character.

All layers is convenient for a simple document. Once sketches, background details, or existing colors influence the detected regions, a narrower reference is easier to manage. Color Labeled Layers lets you choose which labeled layers supply the boundaries. Krita Manual: Fill Tool

Assign a color label to your line-art layer through its context menu in the Layers docker. In the Fill Tool’s Reference settings, select Color Labeled Layers, then enable that label under Labels Used. Keep the destination color layer selected when filling. Layer labels are organizational markers, so choose one consistently for the outlines you intend to reference. Krita Manual: Layers, Krita Manual: Fill Tool

As an illustrative setup, suppose your character has separate outline layers for its main shape and decorative patches. Give both outline layers the same label and reference that label. You can then place their colors on different destination layers while using the same outline reference. Keep unrelated sketch layers outside that label.

A narrow pale fringe beneath smooth outlines calls for a different adjustment from a fill that escapes through an opening. Grow Selection expands the fill region; Feather softens its edge. For crisp flats, begin with no feathering and test a small positive grow value. Milanese’s tutorial demonstrates these controls separately. Francesco Milanese: Krita Fill Tool Basics

Try a two-pixel grow as a starting experiment, then inspect thin outlines and tight corners before continuing. That value is an example, not a universal setting: Krita’s flat-coloring tutorial uses two pixels to illustrate expansion. The same tutorial explains that a low threshold can leave artifacts, while a high threshold can overlook lighter lines. Krita Manual: Flat Coloring

For variable-width outlines, the Fill Tool also offers Stop Growing at the Darkest and/or More Opaque Pixels. It limits expansion adaptively near the line’s interior. Close Gap, documented as added in Krita 5.3, can help contain fills around small openings when available in your version. Krita Manual: Fill Tool

Use this sequence as a practical decision aid. First confirm where the pixels went, then check the reference, and only then adjust the boundary or edge settings. It keeps a visibility problem from becoming a series of unnecessary threshold changes.

What you see	First check	Next action
Color appears only after hiding Line Art	Opaque white in the outline layer	Review Multiply or Color to Alpha preparation
The entire empty color layer fills	Current Layer reference or whole-selection fill mode	Restore the boundary-aware bucket setup
A fill crosses into a neighboring region	An opening or a faint boundary	Inspect the outline; test Close Gap if available
A thin fringe remains inside the outline	Insufficient fill expansion	Test a small positive grow value
Regions follow background or sketch details	All layers includes unwanted reference content	Switch to labeled outline layers

These checks combine the manual’s explanations of layer preparation, reference sampling, threshold, growth, and gap handling. Change one setting at a time and retry the same region so the result remains easy to compare. Krita Manual: Flat Coloring, Krita Manual: Fill Tool

For a difficult region, switch to the Contiguous Selection Tool, represented by a magic wand. It selects connected pixels of similar color and has its own Reference settings. Choose All layers or your labeled outlines, then click inside the region. Hold Shift while clicking additional regions to add them to the selection. Krita Manual: Contiguous Selection Tool

Inspect the selection before committing color. This tool provides threshold, growth, anti-aliasing, and feathering adjustments; its documented Close Gap option begins with version 5.3. Once the selection follows the intended region, select Flat Colors and use Shift + Backspace to fill it with the foreground color. Clear the selection before returning to ordinary bucket work. Krita Manual: Contiguous Selection Tool, Francesco Milanese: Krita Fill Tool Basics

Finish by inspecting small enclosed details, narrow corners, and the outer contour at both close zoom and your intended viewing size. Toggle the outline and color layers independently once more. With the destination layer confirmed and a consistent reference selected, you can continue filling the character while keeping its original line art available for separate edits.

• Fill Tool — Krita Manual
• Flat Coloring — Krita Manual
• Paint Layers — Krita Manual
• Layers — Krita Manual
• Settings Menu — Krita Manual
• Contiguous Selection Tool — Krita Manual
• Krita Basics: How to Use the Fill Tool and Fill Shortcuts — Francesco Milanese