Vertex paint from particle position?

[dantrodgers]

You can use a tySelect modifier to convert selections into vertex colors, and then use your flow particles to do the selection using tySelect's particle selection mode. Finally, turn on additive selections so that the history of selections is maintained over time (ie, the particles will leave a selection "trail" over time).

Then in  your material you can blend with a Vertex Color map.

Awesome!!  Thanks for getting back to me. I'll give it a go.