Rewrite color validation code. Fixes #186 (again)
Rewrite color validation code. Fixes #186 (again)

der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,der-lyse/newsboat,der-lyse/newsboat,x4121/newsbeuter,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,newsboat/newsboat,newsboat/newsboat,der-lyse/newsboat,x4121/newsbeuter,x4121/newsbeuter,der-lyse/newsboat,x4121/newsbeuter,der-lyse/newsboat