Heh, odd, your list of colours is not entirely dissimilar to the colour coding of numbers on electronic components, like resistors. That list is:

0 = black
1 = brown
2 = red
3 = orange
4 = yellow
5 = green
6 = blue
7 = purple
8 = grey
9 = white

Note that this code is partly based upon a normal rainbow, in the range from 2/red to 7/purple. On the low side, you can imagine it going to black over the intermediate colour between red and black: brown; but on the upper side, that isn't so cut-and-dried.