New Haven, Connecticut,: Blue Precancels

Is anyone familiar with the blue ink Type 232 precancels of New Haven, CT? I have one here that looks vaguely blue to me. But more like a blue sheen rather than an obvious blue color. I was pondering it and when I turned it over, someone has actually written Blue on the back.

Does anyone know how different from regular black they look? Also, are they pretty common? Brunell lists them, but minimal difference in "lowest value" pricing from the black ones (25c compared to 15c for black). Is that true of all values (this is a 641 - 9c 11x10 1/2).

Thanks.

I'll leave this up but I kind of answered my own question -- I continued through my New Haven precancels and ended up with 5 blue ones, incl. the 9c. So obviously pretty common! [Side note: a couple of them were really obvious, so that helped, but for the others I found holding them at an angle to the light made the blue color pop more.]