The colours don't bother me that much. A bigger thing for me is if they could make each tile customizable by the user.
So I mean take the hotmail tile for example, it would be cool if we had a choice to have it as a single tile size, or 2 tile size rectangle. Also if we could choose between icons, content to be displayed (ranging from saying just the synced email addresses, to new email previews including possible image for the sender), colour, etc etc.
These options I think would really take the live tiles to a whole new level allowing you to customize them to get the info most relevant to you as quickly as possible.
Also somehow adding controls to some of the tiles would be really good. I imagine it could be like if they provided an optional shortcut into some settings (wifi, network, brightness, bluetooth), when you press the shortcut tile the start screen could shrink and fade into the background like when you long press on a tile. And then a widget like box would pop up ontop showing these options as toggles.
This sort of interface would work really well for folders as well in my opinion, providing another layer of live tiles ontop of the main ones on the start screen.