Is it possible to render text and widgets in a color other than black?
Many widgets will render in white-on-black instead of black-on-white if you set them to "Show Inverted".
If you set widgets to "Show Transparent" you can draw underneath them and have it show through, and thus provide background colors or patterns. The same trick is also handy for making buttons that appear to have an icon instead of text: draw the icon underneath!
Canvases can be drawn on in any color or pattern; you can use these directly or within Contraptions to make colorful variations on normal widgets. The fancy button contraptions I made recently can be configured with color images.
Finally, you can customize Decker's palette, substituting some different color globally for white and/or black.