Greetings!
There could be a more elegant solution than what I’m about to suggest:
You can initiate the monochromatic effect by using masks. If I were you, I’d do some research on how masks work and how to implement them.
Because masks are used for materials, if you can get a basic material mask to work, then when you introduce it into your particle system, you should get the desired effect.
Here’s a link to something similar: