the best way is to use a paint program that lets you specify colors using rgb values (ie photoshop, psp, mspaint?) the usual metric for rgb in these programs are unsigned bytes (either decimal or hex) you just have to convert it to a float.
RGB colors in paint programs are commonly calculated in unsigned bytes, with a range of 0-255. Therefore, you would simply divide the color value by 255 to get a float value for the color.
For example, suppose your RGB color in Photoshop is R=127 G=255 B=53
the float values would be:
R=127/255=0.498 (approx 0.5)
G=255/255=1.0
B=53/255=0.208
Hope that helps.
Edit: Stoopid typos
[This message has been edited by yakuza (edited 11-08-2002).]