How to use the Fill tool
Select the Fill tool from the toolbar.
Choose your fill colour from the colour picker.
Set tolerance (if shown). Higher tolerance fills pixels that are similar but not exactly the same colour. Lower tolerance fills only exact matches.
Click the area you want to fill. The tool flood-fills outward from that pixel, replacing all connected matching-coloured pixels with your chosen colour.
How flood fill works
Connected pixels
The fill spreads from the click point to all neighbouring pixels of the same (or similar) colour. It stops at colour boundaries.
Tolerance
Tolerance controls how different a pixel colour can be before the fill stops. Low tolerance = exact colour match only; high = includes similar shades.
No anti-aliasing gaps
The fill respects hard pixel boundaries. If a shape has a 1-pixel anti-aliased edge, the fill may leave a thin halo. Use a slightly higher tolerance to fill through it.
Tips
Click inside an outlined shape drawn with any bitmap tool to instantly flood fill its interior.
Click on a large plain background area to instantly change its colour without affecting the artwork on top.
If fill leaks outside a shape, undo and close any gaps in the outline with the Pencil tool, then retry.