I would guess that since it is artists talking that she was asking why he chose "Sap green" for a particular portion of a piece of art he made as opposed to another color.
The one difference that stands out to me is that sports coaches are allowed to pick their students for the teams and punish those who do not work. As opposed to most teachers which have limited control over who is in their classes and how to punish them if they are slacking ( besides bad grades ).