Sweet Caporal Pins -- Red or Black Backs?

[UKCardGuy]

I can offer observations from my set. I'm about 82% through the Sweet Cap Pin set. Of the 127 that I have, 6 have red letters. Besides the red lettering, there's different color backing papers.

Out of my 127 pins:

1. 28 have pink backing paper with black print(22%)
2. 31 have blue backing paper with black print (24%)
3. 6 have white backing paper with red print (5%)
4. 60 have white backing paper with black print (47%)
5. 2 have no backing paper (2%)

I haven't chased different backing papers and I haven't noticed premiums attached to different backing papers. But if I assume my set is a random collection (though not a big sample size), the red print is far rarer than the others.