Ashley Tisdale who played Sharpay Evans is a natural brunette in real life. 

 Ryan Evans is obviously dyslexic. He had trouble reading that G-O D-R-A-M-A C-L-A-S-S sign, when some of the Wildcats came to show their support for the school's drama class.

 All the HSM movies were shot on actual location of an high school at Salt Lake City, Utah.That's a Mormon capital of the world. 

  Zac Efron's voice was going through some typical male teenager's changing phase when they shoot the HSM1, so it wasn't good enough for Disney back then. That's why they got another guy, Drew Seeley, who did all the singing in that first movie. Zac did all the singing parts all by himself in the sequels, in HSM2 and HSM3.

  Both Zac Efron and Lucas Grabeel are natural blondes. They both dyed their hair later on in life. Zac dyed his hair brown before they started shooting the HSM sequel, HSM2, so his character, Troy Bolton, without any explanation whatsoever became a brunette in HSM2 and stayed that way in HSM3. Lucas Grabeel dyed his hair black recently, in 2020, to avoid being identified with his HSM character, Ryan Evans.

  Corbin Bleu who played Chad Danforth has a natural curly hair, so there was no need for him to wear any wig when shooting the HSM movies. He later cut his hair short.

  There are no Asian American characters in any of the HSM movies. 

  Some actors from HSM movies are also professional dancers. Zac Efron is not one of them. Despite all the dancing he did all by himself, it was just a dance choreography, nothing more.