The "intervening 'if' clause" means that (1) the ability won't trigger at all unless you control a permanent of the specified color, and (2) the ability will do nothing unless you control a permanent of the specified color at the time it resolves.

This ability isn't optional. When Sedraxis Alchemist enters, if you control a blue permanent and no other player controls a nonland permanent, you'll have to target a nonland permanent you control.