Back in the Acessibility: Contrast, colors, and fonts post, I explained how the color/style preferences changed depending on "contrast mode" being on or off:
Following a suggestion by Matthew Paul Thomas, I now merged the two versions into a single one, using a GtkComboBox.
This new version allows both modes to share all possible options. It also reduces interface complexity by eliminating the need for checkboxes in non-contrast mode.
I'm still wondering whether I will make a list of suggested colors available. I have no idea what they would be. :)