When trying to change colors in Themes, Colors and Fonts you can't enter codes in the box.
More / Manage Site / Themes, Color, and Fonts. Click on an icon to change colors a matrix of color options appears, and at the bottom there is a blank space that says "Enter color hex value". When you click there the focus doesn't remain in the box so you can't enter anything.
This was caused by a recent Chrome update.
A workaround is to hold down the mouse button while you enter text.
Another workaround is to temporarily use a different web browser that might not exhibit this problem.
The Chrome and Sites teams are aware of the issue and it should be fixed with the next update.