Splashing a 3rd color is I am ok with. But Splashing a double Thrashold card is for me pretty much a no-go. Either you need strong fixing (3-4 different ways at least I would say) that weakens your power normally or dam much luck. In my Opinion you lose more games with such cards sitting useless on your hand or missing one of your main colors for too long than you win with it.
So Splash: Yes, if you need to, but dont make the mistake to be blinded by power and try multiple double trashold splash cards.