Particles colour in simulation

Hello everyone!

I set the particles to downgrade from red at the beggining (a hot colour) to blue at the end (a cold colour), but when I run the simulation some of the first frames turns from red to a kind of purple and then red again. My deduction is that some of the old particles crash with some new particles and the first colour (red) join with the old one (blue), that's why it happens. I would like to know if that is right or if it is another cause for it.

Thank you in advance.