Multicolor Planeswalker suggestion

Reyemile

Minor suggests tweak to make mono-color planeswalkers slightly more unique, and multi-color planeswalkers slightly less overpowered:

Multi-color planeswalkers cannot cast cards outside their colors, including multicolor cards.

So, for example, Jace and Gideon could both cast Reflector Mage, but Ajani and Kiora would not be able to. Sarkhan Vol could cast Blazing Hellhound, but not Relentless Hunter or Catacomb Sifter.

It's a fairly minor change and a fairly minor reduction in the available card pool for most planeswalkers, but it gives mono-color planeswalkers access to a few card combinations unique to them.