How to deal with a colleague who won't accept they're wrong
Use impersonal language
Hopefully this is obvious, but make sure that your language focuses on the ideas rather than the people. Rather than

I don't think you're grasping the subtleties of the situation

try

I think that there are some extra complications that need consideration in this case

Ask questions
Rather than taking a confrontational approach, try to adopt the role of the inquisitive student. Rather than

There is evidence in publications X and Y that directly contradicts what you are saying

try

What are your reasons for disagreeing with publications X and Y?

or

I'm having trouble understanding why the conclusions from publications X and Y do not apply here. Can you elaborate?

This will hopefully give your colleague a graceful way out without having to turn it into a matter of &quot;you're wrong and I'm right&quot;. As a bonus, it also gives you a way out if it turns out you were wrong after all (however unlikely that is) or that you misunderstood your colleague's point. But as @R.M. and @CaptainEmacs have pointed out in the comments, take care not to overdo it, or you could come across as either clueless, or patronising.
Make someone else the scapegoat
Rather than voicing your concerns directly, put them in the mouth of a hypothetical reviewer. Rather than

I think there are these reasons for rejecting that argument

try

I think that a reviewer could object to that argument for [reasons]. I think we need to anticipate this using [different argument].