following all the polemics going on on various Internet forums lately regarding the DP3 Merrill's colour rendition and whether it's colours are different or not from the DP1/DP2 pair's, I proceeded to a controlled test that should put this discussion to rest - I shot colour charts under controlled flash light, using different WB, computing all colorimetric values in PS, etc.
In short, the result is that there are in fact differences; especially so if you use Auto WB or WB Presets, where the DP3 is much better than the DP1/DP2, much less so if you use Custom WB in which case, actually, the DP2 and DP3 are very similar, versus the DP1 which stands alone in this case.
I posted the whole test, colour charts shots included, on my blog for your reference:
The Sigma DP Merrils and their colours: the truth revealed!
Hope this helps to clarify things on this heated issue