Melt butter in large sauce pan over medium-low heat
Add marshmallows and cook, stirring constantly until melted
Divide marshmallows in half in two bowls.
Add red food coloring to one bowl and green food coloring to the second bowl until desired colors achieved.
Mix 6 Cups Rice Krispies into each bowl until combined.
Press into buttered / greased 13 x 9 casserole pans.
Top both treats with 1/2 Cup m&m's spreading out evenly
Using wax paper press m&m's into Rice Krispie treats
Let set for 15 minutes
Cut into 2 inch squares