Player Contests

Now that you know about roleplay and making ability checks in Chromatia, it’s worth answering one of the biggest questions that has plagued D&D since its inception:

May I roll skill checks against other players, and in turn, what do they roll to contest it?
-Someone asking this question for nine billionth time

In Chromatia, the answer to that question is somewhat freeform. We prefer the usage of a “gentleman’s agreement” in these scenarios – that is to say, the players contesting one another should determine and agree on the rules of the contest prior to making the check(s), then uphold that result after the check is made.
Our two cents? The ideal way of handling this is using the same model as any other check in the game. First, figure out who the target of the check is. In other words, who is making the action or “attacking”, and who is “defending” against it (if player A is trying to keep a secret, and player B is trying to figure out player A is keeping a secret, then Player B’s action is finding the secret while player A is defending it).
The defending player then determines a DC for the check. Consider your passive score in the relevant skill (like deception), adding or subtracting 5 to represent advantage or disadvantage, respectively, or use the Typical Difficulty Classes table provided in the PHB as a general guideline. 
Once you and the other player have agreed on an appropriate DC, the “attacking” player makes the relevant skill check. If the result meets or beats the set DC, the “attacker” wins.