I have not seen one that colour before Alan.. but depends on surface muck i suppose..
Sanding hardly touches these screeds if they are the sprayed surface ones and not the additive one ..
I have seen some this colour. Or should I say variations of colours. It depends on how much bleed water is produced as the discolouration is caused by this bleed water bringing the plasticisers to the top. These in turn stain the surface and of course if they spread out or are distrurbed by partial re mixing during finishing you get a marbled look. Have seen a few anhydrite screeds with similar marbling but they tend to go every very white due to segregation.