Hi Dirk,
It's quite a difficult question to answer without actually seeing a good quality picture.
Tomatoe paste/puree will no doubt darken the sauce but not too drastic. Paprika will do the same, as will chilli powder. What colour is your spice blend? Most spice blends or mixed powders will usually look an orangey colour. Are you using any turmeric in your spice blend?
CA's curry base will not be the culprit I can guarantee you that, I've used it many many times, and for me, it's one of the better bases on the forum.
Maybe you could post a photo of your spice blend and give us the quantities? From that, we should be able to work it out.
At the end of the day though Dirk, if your happy with the taste, the colour is not really important, but I can see why it would bother you.
Sorry I couldn't be more specific for you mate

Ray
