As I recall Ektascan B/RA is magenta on one side, black on the other - but it's been a while since I brought any out into the light.
Shanghai 400 (a.k.a. ORWO NC500) is yellow on the emulsion-side and a dark red-brown on the backside.
Kodak Vision3 films are pitch black on the backside due to the remjet.
Kodak 2468 is a bright red.
Kodak Imagelink HQ has a purple-ish tone to it when viewed against light.
Lucky Aerial 1021 is green.
Tasma Type42 is dark green.
Especially technical films have very interesting colors: white, yellow, red, green, blue, purple... many of them are almost transparent. Maybe if the more famous films lacked the AHU layer, they would also show nice bright colors.