#251 Color mixer can switch to black unexpectedly

[William Kendrick]

Steps to reproduce

1. Select Color Mixer button from color palette
2. Create a color (e.g., click yellow once for a yellow color); click green check to dismiss
3. Color Mixer button in palette shows your color
4. You can now use the chosen color (e.g., yellow, and e.g., coloring with the Paint tool)
5. Select Color Mixer again
6. Observe color is your chosen one (e.g., yellow)
7. Make no alterations; click green check to dismiss
8. Color Mixer button in palette has unexpectedly changed to black
9. If you try to use the color (e.g., coloring with the Paint tool) it is black

h/t "kentonyanamin" on Twitter for reporting this & posting a video showing how to reproduce the bug.

[William Kendrick]

Should be mended by https://sourceforge.net/p/tuxpaint/tuxpaint/ci/1068a33167fdda8892c437a95c6bcc0f3ef05183/