Opposites

I think that opposites are too ambiguous. I used to hate the idea of opposite day. What is the opposite of green, is it light green, is it blue, is it the absence of color? It could be any number of things. This has been bothering me more lately because my dance instructor keeps telling us to do whatever movement we are doing in reverse. I never know if she means do the steps in reverse order, switch from right to left, front to back etc.