Hard to say. Depends on how often she wears them and how her eyes look without them. Its like a girl dying her hair, am i deceived its not her natural hair color? Maybe, but if she has that color all the time because she loves that color is it that deceiving in the end?
I wouldn't be ok with it. Eyes are first things I notice and I would definitely notice sudden change in eye colour. Different eye colour is not her and I'd be happy with whatever her natural eye colour. No need for contacts.
If he told her "you have really pretty eyes. I love your eye colour" and she corrected him by saying "oh they're coloured contacts" I don't see that being an issue. I'm not sure why though. Guys don't care about eye colours, I wouldn't understand why he would need to wear them (in my case). Just keep it simple
Its kind of like wearing makeup and not knowing her natural beauty. But eye contacts is kind of more over, because it does make a big difference to how the person looks like. It is easy to tell when a person wears colored contacts, it makes their cornia much bigger than the original size.