What is your advice concerning a colleague who has a beard and prays, but is duplicitous, flatters everyone, changes his words, lies, and evades, thinking that this is tact and intelligence to please all parties?

We are advised to verify and to think well of those whose outward appearance is righteous. What has been mentioned could be an excusable matter, as lying has been permitted for the sake of reconciling people. And not confronting people with what they dislike is a commendable trait.

However, if it is established with certainty that he engages in lying and presents a different face to each group, then this is Islamically reprehensible, unless his intention is to reconcile between two groups. If this is his situation, then advise him, for perhaps he will desist, and supplicate to Allah for him.