That could be a problem. Slightly more info here but basically, my focus is going to be for these pellets of PET until I can find another source of Ultradur GFPBT. Obviously such a search won't be necessary if the sample pellets I have are non-printable.
I've found some ABS that is 16% glass fibre filled and comes grey straight out of the gate (I'm aiming for white or grey filament predominantly). Here's the datasheet.