Is it wrong that I'm upset over my girlfriend's panty choice?
How does her choice upset you?
I hate that she bought pink-colored panties.
Your girlfriend should be free to make her own choices about what to wear, especially when choosing her underwear. If you really hate the color pink, you can let her know politely, but don't let her think that you are criticizing her own sense of style.
I wish she'd picked black panties. I just wish she wasn't so stupid.
It's wrong of you to criticize the underwear that your girlfriend wants to put on her body. She is wearing it for her, not for you. You should consider what your underwear looks like and if she likes what you wear.