I think those lines on their left pant leg is their rap sheet. Each horizontal line represents a crime, and the coloring specifies what kind of crime they committed.
Black is most likely murder, since Gamora only has black lines. Drax must have the same lines, but his left leg is not visible.
Blue is propably theft or burglary, and Rocky has plenty of blue lines.
Green is minor assault, Peter has the most of these and he pretty much looks like the idiot who starts fights or barfights. Rocky has some green too.
Yellow is most likely that sex crime with the Gramosian duchess, only Quill has this line, and only one.
Red is fraud. Rocky has the most of these, and Peter has some red too, those two assholes.
I think these lines also funtion as barcodes. Nova Corps officers can easily scan these and get detailed report on each crime. I think its clever.