This is a complex matter pertaining to some principles of gamification. If gamification is what you are aiming for, then your concern might be justified.
According to Gartner, gamification is such a sensible matter, that recent gamified applications were bound to fail meeting business objectives, primarily due to poor design
The cultural aspects are so inextricable, next to the overall principles of consistency and cohesion derived from the particularities of the project, that I won't even name them.
There isn't such thing as a universal principle with regard to color semiotics. According to this article Which color converts the best, there were some studies according to which red and orange buttons perform better than the green ones.
However, this was only an appearence. In reality, color makes little difference on its own. "What is more important is how it changes the visual hierarchy of the whole page, how it makes the call-to-action stand out. Plus additional information and wording of the button itself."
It makes sense.
I have a pertinent suggestion, but I must say that I don't know much about the context of your business and I cannot guarantee that it will work.
Speaking of visual hierarchy, "expert users" represent the highest class, according to your description, so you must find a way to make it stand out the most. You can achieve that through color contrast. Is your background green? Than make that button red, in order to obtain a complementary contrast, which is the most powerful. Then, expert users will pe perceived as dramatically important.
the "intermediate" class should be just a tad more obvious than the one representative for beginners. Once again, the color choice depends on the overall design, in the sense that you should go for a "middle"-powered contrast.
the "beginner" class should be less intrusive, but still in color harmony with the chromatic environment. Something like an analogous contrast.
I hope this helps. If I come up with new ideas, I will update the answer.