http://iscoresports.com/

Does a scoresheet legend exist?

In particular, what does a colored-in strike box indicate?

Thanks!

A colored in strike box means swinging strike. Version 2.0 allows you to specifiy any strike as swinging. Touch down on the strike button like you normally would but instead of lifting your finger swipe out of the button (as if you were swinging) then lift your finger. You can also input an Intentional ball by doing the same thing with the Ball button.

the colored in strike seems to indicate foul strikes. Does it also indicate strike swinging (wiffs)?

Future games will indicate wiffs if that's how you enter it following the instructions above for indicating swinging strikes in the scoring screen. Existing games didnt have that ability so they only show strikes where contact was made.