Im going to buy the XSPC RASA 450 rx120 (120mm rad) kit for my first watercooling kit but thats not the point, I want to have UV coloured tubing and dye for the resovoir but I have the Sharkoon T9 ATX Case (Green version) and was wondering what would look much better? Green UV or Blue UV
Colour scheme isn't something we can really advise on I'm afraid, its one of those personal choices that only you can make, google a few and see which looks better to your eyes, you'll have to live with it after all.
I would advise you against dye though, it can block your kit up and sour your experience so just use coloured tubing and distilled water,
maybe drop a killcoil or a drop of PTNuke in there
although a good dose of UV lighting will help keep microbial growth down