xpColor Object tab menu.
Check this box to enable the xpColor modifier.
Animation to demonstrate xpColor being enabled and the resulting particle change to the Color setting of red.
Set at Independent, by default.
You can change this to Action-Controlled.
In this mode, particles will be affected if they come into the field of effect of the modifier.
When in the Action-Controlled setting, the modifier will only act on a particle when told to do so by an action.
The default mode is Set Color (Immediate) but there are a lot of other options, as shown in the image below.