I know this is a late response, but I've just now been dealing with this issue myself, and have found an answer. Originally I was using Octane as well, but could not solve the issue of having each emitter render with it's own, unique color. So, I switched to Cycles 4D and, after some guidance from the good folks at Insydium, it's no longer a problem. It's all about the Cycles shader, Leaarning the Cycles way of dealing with Explosia-specific volume shaders has been a challenge, but I've got the hang of it and am off to the races.
However, if you have solved this problem with Octane, I'd love to know how you did it.
Here's an example from Cycles: