I'm devastated that perhaps I've damaged my lips somehow. Over the year that I've started playing the trombone, I've noticed the the bottom part of my top lip has gotten paler and paler as though there is less blood flow to the region. I am certain as I can be that I do not play with excess pressure but am still worried that I've constricted the blood vessels somehow. Is this possible?
I'd say your best answer wouldn't come from a fellow trombone player; but more from a doctor. Have you seen the doctor about this? That could be from something more serious...but If I were you, I'd go see a doctor soon.
I agree. You really need to go in and see a doctor about that.
And while you're at it, you should (if you don't already) get a private teacher and ask their opinion about your playing pressure and position. It may just be something you didn't realize. And find someone professional, go to the local major university and ask the trombone professor there, not a college student or local player. Someone with some serious playing and teaching experience.