Very nice find

The following is from Ken Srail's reference collection for the 3¢ Victory commemorative.



Left 2 stamps are both #537 (violet), but different shades. Note there is no clear "red" component. All these violet shades are very common and run a pretty wide range. There are some collectors who specialize in these common violet shades and collect them as plate singles/blocks.

3rd stamp is #537c (red violet)

4th stamp is #537a (deep re violet)

Note the clear red component in both 3rd and 4th stamps. Both of them also have expertizer certificates.

It's always hard to tell from a camera pic with no color reference next to the stamp. But I didn't see a clear red component in your pic, so I defaulted it to #537 color changeling.