Brown stuff sets harder and holds edges better. It's also easier to file. It would be better used for things like hats, tools and non-removable collars. For anything that needs to be clicked over something else then green stuff is better as it has some elasticity after curing. Green stuff also sticks to things better so is better to add details to existing items with.
Everyone knows how slow I am by now, right?
Please, nobody here think ill of themselves!