Encounter at Farpoint (1) - S1-E1
McCoy: How old do you think I am anyway?
Data: 137 years, Admiral, according to Starfleet records.
McCoy: Explain how you remember that so exactly.
Data: I remember every fact I'm exposed to.
McCoy [looking at Data's ears.]: I don't see no points on your ears, boy, but you sound like a Vulcan.
Data: No, sir. I'm an android.
McCoy: Hmm...almost as bad.
Chosen answer: The uniform does indeed change colour. It may be due to the need for a green screen in part, or perhaps some lighting altering our perception. That being said, it certainly looks green at the start, blue thereafter.
The show has been done in HD now and not sure if they fix this problem.
Dan23