Just my opinion, but I think multiple borders look better if they are not the same size. The grass border might look really good if the dark green border was smaller (1/3 to 1/2 the size of the grass border). Think of the border as a mat on a picture. You know how they use a small dark inner mat before adding a larger, lighter colored mat? So, if it were mine, I'd lay the grass border over the dark border leaving just a small amount of dark green showing (2" maybe?) and see if you like it. If so, then trim the dark border and add the grass border. If not, I'd leave it off. But thats just me! :D