Bug 711440 - Tab labels have different background colour than containing gui element
Refactor register color functions to reduce duplication
Rename enum elements to make room for foreground equivalents
Bug 434462 - register color don't work correct with system theme color - Part 1

This commit fixes this for ordinary registers. Entry ledgers (business) aren't handled yet.
Bug 434462 - register color don't work correct with system theme color - Part 2

This commit fixes this for (business) entry ledgers.