I've seen young mobile cooters before but not suwanee cooters. The one I saw was nearly black. But, it couldn't be mobile, because they all have some red invading the head stripes. Top one could confuse people for Red-bellies if they don't see the backward "C" or cusp. Aren't those illegal to sell in Florida?
:interestingly enough, in florida (at least the Tampa area last time I was there) every pet store has tons of these guys for sale labeled as "Florida Redbelly"