alanmt,
a quick google on
WK635 returns these photos of your aircraft in RN colours -
De Havilland Canada DHC-1 Chipmunk T10, WK635, Royal Navy
Photos: De Havilland DHC-1 Chipmunk T10 Aircraft Pictures | Airliners.net
I think there is a TNS specifically about the NATO HI Vis colour scheme that the navy Chipmunks had applied. Perhaps DeHavilland Support can help?
Regards from a fellow ex RN Chipmunk part owner (WP809/G-BVTX)