I think I'm pretty much sold on the Nitron shock. I sent them a email late last night regarding the spring colour and got a reply first thing this morning.
"Our shocks come as standard with our signature turquoise springs. Many years
ago we did offer the spring in black as an option, however we are now being
specifically asked to supply our signature colour. In fact, due to the
racing popularity, there are now several shock copies using our colour
scheme. If, however you would like you own colour, we may be able to
accommodate your request."
But after staring at the picture the turquoise colour is actually beginning to grow on me so I might keep it as it is. Thanks everyone for your suggestions.