I've been looking through some back-issues of the old Scale Aircraft Modelling magazine from the 1980's, as I'm fairly sure there's a cover photo in colour, showing the dinghy hatch tape. No luck so far I'm afraid.
Looking at the various B&W pics, it would seem that various 'colours' might have been used, with the darker colour very possibly the commonly found Dull Red dope, as used on gun port patches etc, and the very light colour might be plain natural linen with a clear dope, used as a sealer and adhesive', the fabric being doped in position in a similar way to hanging wallpaper. If it was, then when applied over the camouflage colours, it could appear as a creamish, 'sandy' shade, or as a light 'dirty' grey, where the dope has slightly darkened the off-white (almost very light grey) fabric.
The Dull Red dope would be used in the same way.