resolveScribbleColor

Resolve one scribble's colour.

A Scribble.color is documented as "a theme colour name or a CSS colour", and the two are told apart the only way they can be: a name that the theme knows about wins, anything else is handed to the canvas as-is. accent — the manager's default — is not a palette entry, so it maps to the selection stroke, which is the colour a laser is expected to be.