White
I think withe is too power, while oters colours as red are too weak.
For example white has all types of magic (block opponent's creatures, power yourself and make indestructible you and your monsters, furthermore, and it is the worst problem, I think, it has mechanics that support themselves (gain hp=power creatures), and this is not possible. One or the othe other.
Other colours have less of types of magic (are more distinct, which is a beatiful thing), for example green and red can't block or destroy with only magic the opponent's creatures, but with green you can't evocate owerpower creatures with only two manas, blue involves magic support: draw and else but weak creatures respect to other colours.
For these reasons I think withe can't call creatures that make you gain hp while it makes 2-3 times stronger your creatures and evocate other creatures, it is ridicolous, while other colours have only few of these mechanics