After reading it up in the source code I found out the formula for particle color:
2^16 * red + 2^8 * green + blue (red, green, blue = 0..255)
I tested it. Correct me if it is wrong.
But it's annoying to type the whole stuff in cubescript every time so I made a gui now to change the particle color.
Add "exec partcolor.cfg" to autoexec.cfg, select a particle entity and write /changeparticlecolor (You should editbind it if you want to use it often. For me KP_ENTER was not used.)
You can select a color from the list and change the color with three sliders. I also added a "bright" checkbox like at the newlight gui.
The right entity attribute will be changed (I also considered that the progress versus particle has two colors). If an ent wich is not a particle is selected the "change color" button will do nothing.
changelog:
-added preview field for the colour and changed the sliders
-added the option to take the player colour and the particle colour or reset to 0
-added an option to save (and delete) colours. Up to 19 colours can be shown. They can't be named, but the text has the saved colour.
-added scrollbox for saved colours
-buttons instead of guiradio
-reduced the number of displayed colours to 9
-added the option to give colours a name before saving them. you can save the same colour multiple times if it has a different name (disable it?)