Questions On 3 1870's Stamps

Just bought an album of XIX century US stamps, and even if condition wasn't good, cannot go wrong for 20$.
I have a lot of trouble using Scott to identify the stamps, especially for the colors and papers (too many choices and not yet used to them) so for instant as European I use Yvert. (I know is not very accurate, but it is easier to classify)

I have a question on 3 stamps:
The 1c. cent has a color dot on the left, is that a plate or color problem?
The 10c. has the outer color almost completely vanished, is that a regular problem?
The 15 C which printing type?

codexluminati,

Th 10-cent stamp likely is missing color because of a worn plate, a common effect.