As Ulf said, HMI colour temperature can vary, however, gradually over its lifetime. The upside is you dont have CT jumping from one shot to the next, it should be fairly consistent across a whole session, so post work is relatively simple.
@Ulf: Do you use Bron FCC meter? Does it help with this kind of issue. I'm thinking of getting myself one.
The FCC is great to get access to some extra settings with the grafit A packs, for HMI not so much as HMIs don´t emit a natural color spectrum and therefore is playing trick on the eye and a meter. CT variation with age is very slowly. As I wrote before it can be found especially at 575W bulbs, may be because they are widely used in show equipment like moving heads and the like where color is not that important.
