Color space of MERL BRDF database?
Was interested in this myself and did some digging, I was wondering if they where spectral, but it appears not (although some interesting work on spectral BRDF is here http://web.cs.wpi.edu/~emmanuel/courses/cs563/write_ups/cliffl/cliffl_spectral_brdf.html )

This chat seems to indicate they are camera native linear, probably with sRGB primaries.

https://groups.google.com/forum/#!msg/pbrt/p9zMvZlaodA/4RD7-We8h4gJ