OMG THIS IS THE EXACT REASON I DONT WANNA WEAR COLORED CONTACTS I IMAGINED THIS EXACT SCENERIO... OK this is a toughie... either way he's probably gonna be put off, but this is what I would do. one day if you two are just hanging out causally at his or your place, just randomly be like... ha ha OK I've gotta show you something... and he'll be like what.. and just take out one of your contacts. then just explain and be like I didn't know what to say when you complemented me before ha ha and just be confident and chill about it and you'll still come off as attractive just someone who likes to change up their style versus someone who wants to cover up their actual appearance. then after that, stop wearing the contacts haha.
Yeah I do think he would be put off because you led him on to think they are real. If you told him right away they weren't real he might get over it, but still see you as a fake.