Roy, I certainly do not profess to be an expert on the subject and I am sure there are many on here better qualified than me to answer but from what I know about corvette colour schemes they are supposed to conform to standard schemes as laid down by the admiralty, the most common being the Western Approaches Scheme.
As usual with wartime colour schemes there was almost certainly a degree of personal interpretation and, as with armour and aircraft, a lot of this would be driven by nothing more technical than availability of paint!
However here is a brief quote from the "Anatomy of the Ship, The Flower Class Corvette Agassiz" by John McKay and John Harland:
A very comprehensive discussion of various camouflage schemes used in corvettes, and tips on painting a model, are to be found in the Lynch book listed in the sources. Preston and Raven's
Flower Class Corvettes includes colour examples of the patterns used while Hodges
Royal NavyWarship Camouflage 1939-1945 explains the rational behind these schemes.
I would also suggest that you have a good look through this forum:
http://theflowerclasscorvetteforums.yuku.com/btheflowerclasscorvetteforumswhere you will find a wealth of information on the subject as well as a large number of very well informed members.
I think at the end of the day a number of modellers interpret schemes in thier own way driven partly by thier own modelling skills and access to accurate information so there may be a degree of variation introduced there as well.