According to the wiki the grit rating are as follows:

Green
5-8 micron, very aggressive

Black
1-3 micron, medium

Yellow
a strop conditioner for leather conditioner only;

the sequence would be: green followed by the black. The green is rated as a rather coarse so I would be very careful with it. The yellow should be reserved for if/when your strop dries up and need some conditioning.