Hi Steve
The RS looks good, shame its ended up being such a money pit
As for the Fiesta ST have you had a test drive yet? if not, I'd definately recommend trying it before you make your mind up. I've had my ST now for about 6 weeks or so. Overall i'm really pleased with it, and glad I went for it.
Plus points, not bad MPG, good performance, good handling, good looks, well equipped, nice gear box, good driving position (good seats), reasonable insurance.
Things I don't really like about it - at 5-6k revs it doesnt pull as well as my ST170 did (different gearing i know) but it also sounds like the engine is struggling a bit. A decent induction kit seems to have solved that, and I'm having a flexi pipe fitted as well which will apparently make a nice difference to the torque at higher revs (pretty cheap upgrades to the car for around £200). Also the car took a little getting used to throwing it into corners. While it handles very well, and the driving position is good (view etc), it does "feel" that its sitting quite high and that you could topple over... but once you get used to the fact it WILL grip its fine.
I looked at the Focus ST as well, and for £200 a month more + higher insurance it just wasn't worth it. The other car I really liked the look of was the Focus RS mkI but at the end of the day its a 3+ year old performance car, and could go the way of your Escort (money pit...).
The Fiesta imo is a cheap, well performing little hot hatch that does everything I need it to do.... and driving it is fun. Mines on a 3 year deal, and I think for the first time in a long line of car ownership I will probably keep it for at least that hehe.
Colour wise, go with what you like, have a look through the various forums theres a lot for you there to compare - my car was dealer stock, so I didnt have a build wait, + I got a big discount on the car, so I only had the choice of black or silver. I think all of the colours look good in their own right, but i'm probably with you on the frozen white - if I'd had the choice it would have been frozen white, full stripes - with black ST being my 2nd choice colour - but I like it a lot.
Good luck with it all, let us know how you get on