Go look at the 1847usa web site. Various differences can be seen in the engraving of the hairs at the top of Washington's head, a narrowing of the width of the oval around the vignette, the shape of the "T" left "Two" and others. The triangles of types I and II are different, but the triangles of types III and IV have the same appearance with no lines between the inner and outer boundary lines. While some shades are found only on the type IV 279B and other minor letter varieties, other shades are common to both.
This is arguably the worst US stamp for color shades, and I am most certainly a novice here with a very small reference library/collection. While I agree with your finding that all are 279B, and with the caveat that judging color here is problematic...
The only stamp which I see that might bear further investigation is the one bottom row center. It might be of the orange-red variety. I'm sorry, but I do not see a rose-carmine here. The top row appears to be red, light red, deep red - all "normal" 279B while the remaining two appear to be carmines.
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