Add a secondary color for custom themes

[gabelipf]

⚬ PROBLEM: I wish I could also customize the color of the header in the custom theme, also I wish the color picker gave me an option to pick hex color values or rgb values

⚬ SOLUTION: Add another color, ie secondary/header color, as well as other options for picking colors

⚬ ALTERNATIVES: add a third color field or even autimatically pick the secondary color, and add an rgb or hex text box

⚬ RELEVANCE / SCOPE: I wish when using a custom theme the layout didn't seem so flat

⚬ "SIDE EFFECTS": none that I can think of

⚬ CONTEXT:
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Thank you!

SHORT Table	(Summary)
Problem	No secondary color option in custom theme
Solution	add that option
Alternatives	pick the secondary color automatically
Scope
Side effects
Context