How to calculate the k (colour temp) of a combination of bulbs?

[kien]

I really don't know the answer to this either so I'll just talk out my arse..

If it were me, I would just take an average. The bulbs are rated at a certain temperature, and since light is additive, it would stand to reason that you could average them together ? Mind you, I have no clue what a fiji purple bulb's temperature would be..