If it's a minor shading issue, apparently Scott doesn't recognize it in their catalog, so it is not likely to be considered anything significant. Could be a "freak" of some sort. In any event, it's always fun to collect these oddities.
Quite honestly, I think your second stamp has a slight color shift (or misregistration), too, as I have highlighted here:

Unfortunately, I don't think any of it will merit any premium value ... it's more of a conversation piece than anything else.