An early assertion of independence comes when our kids want to pick out for themselves what to wear for the day. Since I only had boys, you would think that wouldn't be such a big deal. Compound it with the fact that our oldest is color blind and now you're taking a risk that mismatch will be the fashion of the day.
I have found that boys don't have as many varied clothing choices in their closet or drawers as girls do. There are more chances for things to go awry when young girls pick out their own clothes than boys. I've met many a mom who just aren't willing to take that chance and retain the clothing choice authority for as long as possible - sometimes to the extreme.
Years ago when I was teaching middle school, I had one young lady whose parents forced her to wear a uniform to school even though the school didn't require uniforms. Their control over what she wore was tighter than airport security (maybe that's not saying much though). Becky always had a change of clothes stashed in her locker at school. She changed right before first period. Unfortunately what she changed into wasn't always appropriate. I believe Becky was exercising her right of clothing choice in a desperate way. Maybe this is why her parents made her wear a uniform in the first place. They didn't trust her choices.
It's important that we give our children choices while they're still with us so that we can let them make mistakes when the stakes aren't so high. Teach them what's appropriate and what's not, but allow them to learn what that looks like for themselves.
When they're three or four or five, if you let them pick out their own clothes, the worst that could happen is they mix plaids with stripes or want to wear the same princess shirt every day. In our son's case, he wore purple and blue because they both looked black to him.
Look for ways to let go of your control over what your kids wear early and often. Even if their choice is appropriate it may not always match. And that's okay.