As you're in the UK you will be able to find Abys in a range of colours - the ones currently accepted are: usual (black ticked), sorrel, blue, fawn, usual silver, sorrel silver, blue silver, and fawn silver. Chocolate and lilac have provisional status in the GCCF so may also be available, but can't be shown in championship classes at present, which may be a consideration if you fancy showing. There are other colours that crop up that aren't yet accepted or only have preliminary status so can't be shown including red, cream, and tortie, and silvers of those colours also.
I was really taken by a usual silver aby that I saw at a show, absolutely stunning colour in my opinion
Edit to add: Your Cat magazine has just done features on both the Aby and the Russian Blue - the Aby was in the April 08 issue, and the Russian Blue was March 08, so if you haven't seen those it may be worth ordering them as back issues
Editing again: Sorry I have edited this several times to try to describe the colours and their current GCCF status. I'm sure I've been a bit confusing, so here is a link to a table showing the colours available and what their current status is in the GCCF. Other registries in the UK such as TICA and FIFe will not be the same, but most breeders are GCCF registered.Abyssinian colour chart, UK colours