Thank you all you lovely ladies for taking the time to reply. Well after doing a few little experiments on this, it seems that actually I did get a better result/silver colour spraying directly onto the white!! Would you believe though, after all this, that my airbrush even though only a couple of months old & barely used…stopped working:( I may end up having to use the silver sheen colour with a a paintbrush…very disappointing (do you add vodka to airbrush colours when hand painting with them?) However, for future reference, I would definitely now say to spray colours directly onto white fondant. Thanks again for your input guys, very much appreciated.