But the Earth's moon is greyUnfortunately, planets without atmospheres seem to tend towards browns and greys. FD's intentional change might have things looking pretty accurate. The question might best be phrased as: should FD change it simply for aesthetic reasons, or leave it as it is for sim reasons?
As noted above though, pluto is kind of brownish-grey, mars is more reddish (but apparently only skin deep).
Maybe FD can tweak things a little to give a little more variety, without going overboard.