I wouldn't go with 2 Blue and 2 Purple. That's a lot of red light.
I would look at 2 Actinic Blue and 2 Aquablue from Gmann. If your store uses Gmann bulbs over tanks, see which Aquablue you like more. They have the Azure and Coral. From what I can find online, the Coral is the better of the two but the Azure supposedly had some changes in the last couple years. I tried one of the original Azure bulbs and it wasn't what Gmann claimed at all. It was supposed to be a turquoise look but it was pure yellow and made things look terrible. Again, the new one is supposed to be very different so see if your store is running it anywhere