Well seeing how OAW was noted for light blue rib tapes, I would go with that. Perhaps the restoration done in the 1960's did not follow actual fabric covering practice, or by the time that it was restored the original fabric was already missing? As we can see in the modern photos, the lozenge as it now appears has lower lozenge on the undersurface, although if you look at the previous thread on rib tapes it says that the rib tapes were same color top and bottom wrapped around the leading edge.
To find the truth we need to find a clear photo of the aircraft from 1918...
Here is one that I found posted by James vanWyngarden on the Aerodrome forum, and the rib tapes on the top of the lower wing are definitely a single light color, and since it was OAW built that would lead me to conclude light blue is correct.
Dave