I am trying to change the color of a particle when it comes in contact with an colliding object. Iv'e tried using the particle event editor, but that creates a new particle. Can anyone tell me how to achieve this using only one particle.

say suppose the initial particle color is red, it should become blue when it comes in contact with the colliding plain and should remain blue(and should not change color while it is rolling down) until it touches another object.

I tried changing the particle name to EVENT and wrote a script so that the particle changes color as the event changes. But the thing is, when the particle rolls down each contact with the plain is considered as an event and the color keeps changing.

Could someone help me out.
Thanks.