I never thought of the whole same color thing...
Originally I had a small 20 gallon tank with guppies but I aparently am guppy kryptonite and could never keep more then 4 alive. Eventually I was down to one guppy who is indestrustible so I dropped him into the bigger tank with the tetra and corys hoping he would be happier. It worked he schools with the tetra great and doesn't get bullied at all by the larger fish. Maybe it's due to the fact that he and the tetra are all red.