Black grout should definitely be banned, just as others have said I also keep a separate bucket, sponge & stained float for it, after having to bin a couple of each in the past! White / Ivory on walls, grey on floors. Those are the rules!
IMO your next step should be to get one or two recommended tilers from a local tile store. Or as above and advertise the job on here & get a suitably experienced tiler come and quote for the job.
Just to update all that have posted, the guy from Topps was stumped after trying a couple of different cleaners. I got a friend to come have a look - an older, slightly wiser tiler - and straight away he said it was polymer fibres from the grout. Fila deep cleaning stain remover cleared the haze...
It was Fila Grout Residue Remover Honed & Polished Stone that was used, also tried a clean warm water wash, to no avail.
Cam_low they cut slowly! To prevent any risk of chipping the glass I scored first then ran through the wet saw, got lovely clean cuts each time but just took an eternity.
Ok, so the residue remover for polished stone didnt work, neither did the tile & stone solvent equivalent!
I did attempt to take pictures but because of the tiles being glass over high gloss porcelain, they're just too damn reflective. All that can be seen is me with Samsung in hand & the rest...
I'm fairly sure that Montolit or Raimondi (under the same umbrella, I know!) sell an alternative the levelling system, a tile beater or lippage plate I think its called.
The haze does look like its in or under the glass, yes. Ive spoken to Fila this morning and was told their polished stone residue remover should bring them up to a finish. Unless I'm informed otherwise thats what I will try on saturday morning & will of course update on here. Hopefully with pics...
Dave, I'd have to say its a haze, but a streaky haze!
As for cutting, I havent used a Rubi since I became a convert 3 years ago - Montolit all the way for me. Even with their
superiority I found these tiles were still a real pain, some would score & snap ok then you'd get some that sheered off...