Thank you for the reply but that's not so good for me.
First thing first I'm one of that dudes that hates to have extra stuff on the pc and keeping the Custom Tiles app just to have a function who was already in the system is not the best to me.
Plus, the right click on the corner to get the extra funcions has always been there in Windows 8 so no big news here either. Right know I'm keeping the tiles like this because I have too much stuff I'm working on to format my computer but I'd definitely do that to change this horrible looking rainbow.
I think I might be confused somewhat. You want to change the color of the tiles, or the background they're placed on?
My confusion stems from your reference to the ugly rainbow which is one of the lock screen images.