When getting dressed this morning, Erica chose a skirt with blue and purple flowers. Then she wanted me to choose her shirt. I pulled out a purple shirt. She said no. I pulled out a blue shirt. She said no again. I told her to pick her own shirt and left the room. A few minutes later, Erica came out dressed. When I said that the pink flower shirt didn't match the blue and purple flower skirt, Erica said, "But they're both flowers," in the most matter-of-fact way.
So if you see Erica, or another 3 year old, in the store with an odd outfit, you should know that she did in fact choose matching clothes, just according to her own rules.