Your colleague is telling a wrong info to a customer, and he insists that he is telling the right info , how you will handle this situation ?

Looking at the question, I can only assume you have addressed this with your colleague and they still insist it is correct. For the sake of the customer and your colleague and of course your company, gather the required information to show it is wrong and share with your colleague. They might be upset however for the good of all, the sooner you show this information I am sure they will appreciate your efforts. Data is so important to get a message across, sometimes or most times helps people to understand better.

Can tell the colleague separately afterwards when he is done with the customer. As interrupting in front of the customer may ruin his/her relationship.

In case the situation is unpleasant, apologize with the Customer for any inconvenience and in parallel give an indication to your colleague so that both parties get cool down.  Offer them glass of water then listen to Customer, giving priority to Customer will place you on upper hand, afterward ask your colleague which will help you in analyzing the correctness.  Such approach will certainly turn into pleasant and healthy environment.

Whole idea is to keep the Customer relationship and satisfaction up to the mark also to maintain your colleague as well as Company’s reputation irrespective who is right and who is wrong.

There two sides to every story. Here what the customer has to say and compare with employee then decide. Its what good leaders do.  

first try to make sure that  your idea is correct, then asking for an interrupt and share your idea with the colleague privately ... and then after clarify it with customer. but definitely customer must be aware of the right information.

seek permission and interrupt for a while.......it is a rare case indeed because the customer care representative are usually equipped with much info on how to deal with a customer and the problem solving techniques.....

Are we talking about retail or about a key account? it is not the same treatment at all...selling a pair of socks or selling ten million pairs of socks?

In the former case, I would tend to not interrupt my colleague and inform him later of the mistake, in the later case, I would take some action definitely.

Just in case I didn't understand the question, is the customer right and your colleague insisting with a wrong information?

There is a conflict of interest between employee and customer & collegues in this case for or selling a product or commodity,.It requires diplomacy so that nor our relationship with our peer get worse and customer returns home satisfied.Either we can ask our collegue aside to stop making false claims, then he still pursues we need to raise issue with manager.However misleading consumer is against fair consumer act concept

i will excuse my colleague so that i explain in private where he/she is going wrong,failure to make him/her understand i will take over and tell the customer the correct information without making my colleague look bad