I did the quest so you can train colossal in zafaria and it won't let me train it does anyone know why it's doing this?
Did you meet all of the "requirements" ... are you Level 64? Did you train on the "other" spells first (Strong, Giant, etc.). Just like on the lower level spells back in Ravenwood, we can't just pick and choose which spell we want. We must train on the lower level spells first.
This link gives all of the details for Colossal ("requirements", etc.):