Re: Really weird Continuity error. HUGE SPOILERS!
Thing is Spock Prime looked the same when he was still in the Picard era and on Romulus in 2387. The mind meld flashback shot of him speaking with Romulan leaders about the supernova crisis shows the same hair color that he would sport after he was thrown back in time into the altered history.
A fun little theory, but it doesn't jibe with Nimoy's appearance when his character was still in the original 24th century.
Human instinct is pretty strong. You can't expect us to change overnight.
-Captain Jonathan Archer, 2151