Hi James -- I'll say the lab is veering around trying to find a neutral color balance while printing your B&W order on color paper, and not doing very well! Chromogenic films that have an orange mask can be printed on color paper with little or no operator adjustment, and come our relatively neutral. But Ilford XP2 has no mask, and prints best on B&W papers. Certainly, if the lab is willing to make the effort, XP2 can print fine on color paper too.
I'm very fond of Ilford XP2 Super, having begun using it a couple decades ago when it was XP1. I prefer the lack of mask, making it much easier to print in my darkroom on multi-contrast papers... which use magenta and yellow filters to raise and lower contrast. Orange mask throws that for a loop. Also, I suspect the density of the mask reduces the dynamic range of the film.
XP2 has a very wide density range and tends toward lower contrast. Especially for shots in low contrast lighting, prints tend to look dull. In printing, a #3 paper grade is about "normal". But the lab won't do that; you'd need custom printing.
That's the downside... The good thing about this is that the film records a broad range of light and dark, giving you lots of flexibility in printing and scanning. The data is there, your job is to deal with it how you wish. It's easy to bring the scans to life with a tweak in the histogram control.
Chromogenic films, and I think C41 process films in general, are not happy with underexposure: The shadow areas go all flat and grainy. But they're very tolerant of overexposure. Almost impossible to totally block up the highlights; it may take you some work to display those highlights, but the data is there in the neg.
And a generous exposure seems to smooth-out the tonality, for a characteristic creamy richness. So I set my meter to give 2/3 stop more than the manufacturer recommends; EI 250 for an ISO 400 film. Or you could just pay more attention to metering the shadows to make sure you retain detail where you want it.
