Add option to select a pallet for colors

[kunaltyagi]

For certain remote hosts, I'd like to restrict the random colors to 256 color pallet, commonly used in the 256 terminal color

This way, I can set the theme of the terminal to be the same as the editor.

Ofc, the color can be chosen manually, but having a shortcut without adding 256 favorite colors would be really neat

[johnpapa]

Thank you @kunaltyagi for creating this issue!

[mattgauntseo-sentry]

I would love to be able to define my own favorite colors for peacock. Would you be open to guiding / accepting a PR for this?