iMovie title color will not change

Whenever iMovie stops behaving correctly one of the first things you should do is delete the preferences.

Launch iMovie whilst holding down the Option and Command keys until a window pops up asking whether you want to delete the preferences.

Click the Delete button and iMovie will open.

I assume it "got there" because that's where it was all the time. You had probably inadvertently set that Library as the destination.

When you trash the preferences iMovie sometimes opens with an empty project but the projects are perfectly safe as they are completely separate from the iMovie app. You just have to navigate to them and open them.

Remember to delete the preferences whenever anything unusual happens with iMovie. It won't always cure the problem but it's always worth trying.