Hi Allan!
THe original colour was plychromatic green, which nowadays is called "metallic paint".
Literature states "Toyota Altair green" as a substitute. This was used for the first Celicas and is no more available today, at least not here in Austria.
So I spent searching hundreds of sample cards at my local painter's, comparing them to a mudguard with original paint, and what I found are the following alternatives:
1. Daihatsu G27 light green /D. (from 1998). There are two tones of this colour available, the darker shade is the closest match I could find.
2. Rover HQJ/GM cimarron green (from 2004). This is the next best match, should definitely be available in the UK. As far as I can remember, it was pretty close, too.
If you don't have a direct comparison to the original paint, you won't notice any difference. But from what I could tell, the original paint didn't have as many metallic particles as the modern paints do, so the "glittering effect" in direct sunlight was not so distinctive. Well, it's something I can live with, but if you have the paint mixed up for you, maybe they can reduce the metallic effect a bit???
Hope that did help.
Regards, MG