Add color indicator

Any chance to add some indicator for color, something like we have in palette.js addons:
http://www.jeditoolkit.com/CodeMirror/demo/palette.html

This can be optional, and if turn on then it should be synhronized with slider, when we change color then coresponding color indicator will change too. This can be very useful to faster orientation for a visual representation of any declaration of color.

Start by reviewing the palette.js addons example linked in the issue and the repository's existing slider and color-picker behavior. Define the optional color indicator's placement and synchronization with slider changes; done means the indicator updates whenever the selected color changes and can be enabled or disabled.

Written by the indexing model from the issue text.