It is quite hard to help another person over the internet. Do you have a local reef club in your area? Make some friends and ask the more experiences reefer to look at your tank. It is much easier for them to give you advice once they see the tank. Anyway, your tank is a standard 75 gallons tank, so the height is 21"? Your light fixture isn't the best quality and it is only using 4 bulbs, so I think it is a little bit underpower right there. is there any way you can borrow a Par meter and measure your par? Also how many hours are you running the light? I looked at your build thread and you only have a few small sps in the middle of the tank. I don't think they are getting enough light. To get color out of sps, you just need a clean tank (By clean, I mean low nitrate (0-10) and low phosphate ( Less than .01). different people go by different number and ranges for these nitrate and phosphate. I am able to get most color out of my sps EXCEPT red. The color are quite bright and vivid as well. All that I do are changing water once a week (10%), run carbon and GFO to keep the algae in control, Feed fishes twice a day with frozen foods and keep Alk stable around 9.
Anyway, like I said it is quite hard to give advice since we can't see the tank. The one thing I would improve is the light if I want to keep SPS. a ATI Sunpower 6 bulbs would be Perfect for that tank. I used to have the same tank and lighted it with Sunpower 6 bulbs. I can grow sps pretty much anywhere with that light.