Could Pontus have ever had a colony in Thracia? I mean Thracia is right next to them and it would only further secure Pontic influence over the Black Sea. Plus Thracia already had a Greco-Thracian influence because of trade with Macedon, and other Greek city-states.
I might be wrong, but wasn't Thracia already controlled by the Romans at that point?
I think that during Mithridates VI they had some small costal holdings but I doubt that they could get more than that given that Pontus would never invest many resources on Thrace when Asia minor and Crimea were they main interests.
So what if Mithridates VI did invest more into Thracia? The Thracian tribes could even just be incorporated into Pontus because many didn't want to be part of Rome. Had Pontus invested more.