I wrote the script below to change weapon particle effect colors. It triggers on the change of color of the prim in which it resides. So, you can set the color using the SL color picker, and the exact color vector will be sent region wide to a receiver. Then, you can pass the color vector to your particle script as discussed above. I also integrated this script with a menu system that had nine preset colors. as well. But, this script will give you over 16,500,000 colors.
Hope you find this useful:
integer CHANNEL; //Channel for sending color ve