That’s exactly as @FraVit93 said.
Making some examples just to be clear:
you bring only Quintus as purple in your team: all tiles are “Quintus tiles” so you have tot % to trigger his class skill
you bring Sartana and Quintus: half of the tiles are "“Quintus tiles” and half “Sartana tiles”. So you have half chance has before to trigger Quintus class talent, and half of Sartana talent
you bring Quintus and Sabina. Half of tiles will be Sabina’s and half of Quintus, but both have the same class talent, which result as you had bring Quintus alone (but with more tiles damage)
So same colors can only reduce the chance of triggering sorcerer and barbarian tiles, but different colors (with same talent) increase that chance.
Edit: need to add that Quintus and Sabina tiles results in the same chance of triggering sorcerer talent only if BOTH were already class upgraded.
If only one is class upgraded then again you have half the chance.
If they are differently upgraded, half tiles has Quintus chance, half Sabina.
And so on…