Hi Neil
This is a very interesting topic,
My answer is , sorry i dont know !!
I had a look in my old 22 handbook and dont see any mention to black for 22 and red for 28, however this may of happened back in the day,
I know there are lots of different colour "seals" and sail numbers out there, mainly blach blue or red
also someone recently asked me the question was there a particular size for the seal, to which i replied, al long as it looks in proportion then ot should be ok.
My 275 "Sophia" being a blue hull, with blue dodgers,and stackpack has as blue seal and sail numbers
Many earlier 275s, 31, 325s with the red/grey strip decals have red seals and sail numbers to match, and hulls with the blue decals anr blue or black,
I suspect earlier 26s and 27s have logos coloured to match their spray hoods and dodgers which is at the decision of the owners at the time.
When i bought my 26 back in 2000, she had black strips and her name was black on the topsides and had a black seal and sail numbers,
I changed her from black to a blue (sacrifial strip on jib was blue) and when i bought new sails i changed them to blue to match.
Perhaps vintage members may be able to shed a bit of light to this
Cheers for now
Peter Lowry