[frio] simplify scheme accent color UI

[foss-]

Currently

Expected

• rename Select Scheme Accent to Accent color ([frio] Remove legacy schemes #13948)
• no need to name the colors, remove that info
• increase size of color bubble
• make color bubble interactive and show checkmark for selected color

Much user happiness.

[MrPetovan]

add 6th highlight color to have a symmetric value when showing highlight colors

Ah yes, just add a color, not that it took me forever to find the right combination of CSS values for the existing 5 in both Light, Dark and Black schemes 😭

[annando]

Now you are experienced in it, so it shouldn't take much time ... 😁

[MrPetovan]

This isn't a Role Playing Game!

[foss-]

18/20 experience in color CSS values: Roll the dice -> You create an awesome new color picker UI for a decentral social network. Congratulations.