xfdesktop4: Re-add and fully implement primary colour changer

[1280px]

opened on May 6

I scrapped the prototype a few commits ago, but I think it'd actually make sense to have it implemented, simply add a line to reset the colour pattern to solid fill as well. The biggest obstacle for now, though, is I can't figure out how XFCE actually stores RGB colour values (it's like an array but actually not?...)