Another little detail I've heard from buyers at other dealers is that the carpet mats are Black no matter what car you buy. This is not true, Toyota makes them in dark gray and misty gray as well as black but those are usually special order items. My dealer, Royal Palm in W. Palm Bch, Fl special ordered matching gray Original Toyota Prius mats for me, at a price below the aftermarket mats I've seen advertised. They'll be here tueday, or two business days after I bought my car. Unfortunately there are a lot of buyers who don't know this (and salesreps who either don't know or don't want to walk over to the parts dept and order them). So buyers are driving away with a mismatched color combo inside their car. If you have a gray interior and want them, ask your dealer to order the matching gray mats for you instead of the black.
Dark gray already has matching mats. Misty gray has matching mats the same color as the leather door panel inserts and center console top, which provides for a more sporty look. Bisque owners may want to go for what the OP suggested if they don't like black mats.
I know of one new owner who got Bisque mats in his new Grey prius! You have some good info. here for others who get stuck with the 'wrong' mats.
PriusTeam (toyota marketing) and online info made it clear there are no bisque mats (not talking about cargo mats) for prius - just light grey, dark grey and black. Your anecdotal owner either has light grey mats or non-Prius mats.
I have dark gray but picked black on purpose because dirt is black (and picked dark gray because of the three interior color offered, obv. it was the closest to dirt)
So you can special request a certain color floor mats? Hmmm.... I'm getting dark gray leather, which will come with the dark gray floor mats, I'm pretty sure. Maybe the black floor mats would look cool... Wish I could see both of the combinations first