Or is it too much of a stretch? I know [name]Colin[/name] is a diminutive of [name]Nicholas[/name] but I also know most people don’t know that haha. Thanks for the advice! 
I think it’s too much of a stretch. [name]Cole[/name] can work as a nickname for [name]Nicolas[/name] because the sound is in the middle of the name (nic-cole-us) but [name]Colin[/name] just seems very unnatural. Since [name]Colin[/name] is a full name in its own right, I would just use that up front if that’s the name you were going to use the majority of the time anyway.
[name]Way[/name] too much of a stretch. [name]Colin[/name] is a full name in its own right, and like the pp said, I would just use [name]Colin[/name] if that’s the name you’d be trying to call him most of the time.
I third the previous opinions.
I agree with pps: [name]Colin[/name] may derive from [name]Nicholas[/name], but it doesn’t really work as a nn these days.
I feel like most people out side of nameberry (;D) won’t know that. I think it will be too much of a stretch irl. What about [name]Cole[/name]?
I think it is a stretch.
Huuuge stretch
Agree with PPs. I don’t think it works. I like both names though. And I actually really like [name]Nico[/name] for [name]Nicholas[/name] 