There is a possibility that they were a colour other than 'Sky', but all references I have give the colour at the time as 'Sky', for UK and BAFO aircraft, and I haven't seen any evidence of other colours deviating from standard specifications. The airframes were finished in the standard scheme as of January 5th 1945, although of course 80 Sqn didn't receive the Mk24s until January 1948, and certaily RAuxAF Mk22s had 'Sky' codes.
However, as this was the only regular RAF squadron operating the type, with most other fighter squadrons having converted to jets, it is possible, if not probable, that the codes could have been white, as they were on bombers by then. Interesting that the original Matchbox issue of the 1/32nd scale Mk24 had white 80 Sqn codes, as does the same kit, re-released under the Revell lable. I've just checked some other refs of colour profiles, and they also show white code letters for this squadron, with B&W pics also showing what appear to be white letters, but I still can't find any reference to blue codes, or blue and white codes, other than the one mentioned on the raf.org web site.