What colors do you use for each of the rupee types? (1, 5, 10, 20, 50, & 200)

I'm going to have all of those rupees, plus a custom 2-piece & 100-piece rupee (using the zxxx items) I'm just wondering what colors i should use.

I'm thinking of doing the following:

Green--1 piece
Orange--2 Piece
Blue--5 Piece
Red--10 Piece
???--20 Piece
Purple--50 Piece
Grey--100 Piece
Yellow--200 Piece

I've run out of colors for a 20-piece rupee.