XLD, I changed one of the other colors in the range you specified and it's still behaving the same way. It doesn't seem to be honoring the same set of colors at all, because I changed color38 to the my custom color and it still chose the color from the original set instead of my custom color.
If you go into Tools > Options > SAVE settings > then click on the COLORS button it will show you the color window that the [color] feature follows in formulas, but it doesn't seem to be the same for charts.
Note: This works as expected in Excel2003, but not in 2007 or 2010.
