The tolerance slider is one of the most important features of this coloring tool. It determines how similar a color must be to your starting point to be included in the fill. At a tolerance of 0, the fill will only replace pixels that are an exact color match - this works well for images with solid, uniform colors but may leave gaps in areas with slight variations. As you increase the tolerance, the fill becomes more permissive, including pixels with increasingly different colors. For most standard drawings, a tolerance setting between 20-30 works well. If you're working with scanned images, photos, or drawings with textured or gradient fills, you may need a higher tolerance of 35-50. If the fill starts bleeding through the lines into adjacent areas, your tolerance is too high and should be reduced. We recommend starting at 28 and adjusting up or down based on your results.

Fill bleeding usually happens for three reasons: the tolerance is set too high, the lines in your image aren't completely closed, or there are gaps in the line art. First, try reducing the tolerance setting - this makes the fill more strict about which colors it replaces. Second, examine the area you're trying to fill - if there are tiny gaps in the lines, the fill will escape through them. You can sometimes fix this by clicking the "clean edges" button, which strengthens the lines. Third, try clicking in a different spot within the same area - sometimes the starting pixel might be in a slightly different color region. If bleeding persists, use the undo button immediately and adjust your approach before trying again.

The tool maintains a history of your last 20 fill operations. This limit ensures good performance while providing ample ability to backtrack through your creative process. Each individual fill counts as one history entry, so you can undo up to 20 separate coloring actions. The history is automatically managed - older states are removed as new ones are added once you exceed 20 actions. This system works independently for each coloring session, and resetting the image clears the history and starts fresh. The undo/redo buttons provide visual feedback by becoming disabled when you reach the beginning or end of your available history.