Green shorts be damned

My son is now sleeping in his underwear on a regular basis. So I'm considering that a win. He no longer insists on wearing a long sleeve shirt over his short sleeve shirt when he goes to pre-school in the morning. Another win. He's stop wearing socks with his sandals. Score. Now the only remaining vestige of operation modesty is his choice of bottoms. He still would rather wear pants to school everyday. One day he randomly agreed to wear his green shorts to school and when we arrived, all of the teachers cheered. I'm not joking. So the next day I took out the maroon shorts that are exactly like the green ones. He wouldn't wear them.

Him: I want green shorts.
Me: The green shorts are dirty honey.
Him: I only wear green shorts.
Me: But you peed on them yesterday so you can't wear them.
Him: ONLY GREEN!
Me: What's wrong with these? They're exactly the same except the color.
Him: I don't like them!
Me: Why not?
Him: I don't know.

You can see how I'm getting nowhere with this argument. So I bought him another pair of green shorts, same shade - apple. And I bought a pair of gray ones too which he refused to wear.

Me: But they're like your gray pants!
Him: No they're not. They're shorts. I only wear green shorts.

Where does he get this stuff? The other day he told me he was willing to wear black shorts too.
I'll just be happy he's not sleeping in fleece.