Spitfire P9374 belly colors

The half-black, half-white underside colors on P9374…was this standard for Mk 1s, or at least used on many, or was this some kind of experiment to see which color worked better? (I’m doing a piece on camouflage for a military-history magazine in the U. S., and this is an interesting example of the craft. it may well be an intentional divergent-colors camouflage.)