Easy fix if yellow was present........
It was.
I don't have an exact date, but they are visible on RAF aircraft in the mid 1930s (unless orthochromatic film was used!).
We do have the painting instructions for the repair of Rotol blades, which gives an idea of how it was originally done.
PAINTING.
38. After repair of covering, except Emergency Repairs, the repaired
parts shall be painted.
(i) Spray or paint with Grey Surfacer and allow to dry.
(ii) Spray or paint two or three coats of Matt Night, DTD.751/4.
(iii) The four-inch yellow tip should be given two or three coats
of Identification, Yellow DTD.751/5
(iv) Paint a White line, 1/32 in. wide at 0.70 of the original
radius, across the thrust face of the blade.
This line indicates the blade pitch angle checking station
and should be at right angles to the longitudinal axis.
(v) Blade identification markings should be made good.
My bold.
Bear in mind that 4" at 1/72 scale is just under 1.5mm.