Blue cast in pictures I believe caused from recently painted studio floor

[Chris Gahran]

I go on location to a client's photo studio every few months. They recently re-painted their white floor as they have done in the past but this time they applied a clear protective coating on top of the paint. Even after neutralizing the camera in Phocus using the "Digital Grey Kard" I've been using for two years, the images require a little red and some yellow to correct the subject color. The white floor becomes warm but the product looks good.

I'm guessing the blue shift is caused by optical brighteners in the clear protective coating. (UV brighteners?) They tell me they painted the floor with the same white paint that's been used for years. The only difference is the protective coating applied on top of the paint..

It appears I need to buy a clear UV filter like the Heliopan Bay 60 UV SH-PMC Filter which is a Multi-Coated, Schott Glass filter that "Absorbs Ultraviolet Light and Reduces Bluish Cast". I don't think a "UV Haze Filter" or "Skylight Filter" will be effective. Some Haze or Skylight filters have a magenta tint.

Any suggestions?

Chris
Phocus 2.6.6, CF-22MS, Hasselblad 555ELD