STOPTHIS said: When you use a different version of that character and match the wrong colors. It took me a while to not match blue or black tiles with 3* BW expecting her to do extra damage. That Hulkbuster can't use yellow.
You're playing a node with CM 3* essential, and you keep getting confused when matches in the opponent's strongest color aren't getting you AP in your strongest (and damaging the opponent team when the colors are the same).