[Feature] Treat pattern-filled areas like solid color

[lafoxxx92]

Steps:

1. Change theme to New Year
2. Select Pattern color (one of the right ones)
3. Draw some lines/fill some areas
4. Change color
5. Attempt to Fill the Patterned area with the new color

Actual:
Only adjacent pixels of same color are Filled with new color

Expected:
All Patterned area within specific boundaries (image/shape of other color) is affected by Fill tool, not just some lines of same color.

Implementation suggestions (not sure how it works, might be not relevant):
Use some special (invisible) color to render the Pattern over it, treat this special (invisible) color like the regular color when editing.

[Isaiah Odhner]

This isn't how MS Paint works, with patterns in Black and White mode, and I don't plan on implementing it. It's complicated, although you suggest a reasonable way to do it, but there are merits to it working either way. Replacing a pattern may be intuitive, but it's also nice to have it simple and consistent, with no hidden semantics of a pixel belonging to a pattern or not.

Consider what happens when you save. Either:

1. It would save as a special color like you describe, and not show up as a pattern, or
2. It would show up as a pattern but when you load it back into the app it works differently, where you can no longer replace a pattern with a new color.
3. Or a new format could be introduced that would store this information, but still loading a "plain" image would be inconsistent with loading this new format.