first off mate dont look for a colour.you are better going for the best cleanest example you can find.
although,if i was to buy i would want polaris grey or gloss black.

as for st/bt....the st engine is better,stronger and should be more reliable and now is just as tunable as the bt but both are good anyway.

there is alot to look for to be honest and if i were you i would scrape together 15k also to make sure you get a goodun.a cheap one will cost you a fortune very soon no doubt.

and take someone who knows them with you!

oh and try www.escortrscosworth.com for more info and very helpful,friendly people