1) I regrouted a section in my bathroom with sanded grout, since the
gaps are about 1/4 to 3/8 inch with 12 inch tiles. I waited the full
2 weeks for grout curing, and then sealed with silicone based sealant
recommended for use on glazed tile (which this is). However the grout
still changes color when it gets wet, which none of the other grout
does. I thought the sealant would protect against this. Am I wrong
or do I need another kind of sealant, or just more applications of the
same?

2) The corner grout where the bath tile (4" tiles) meets the floor
tile (12" tiles) is cracking. Can I tear this up and caulk this
corner joint instead, or if I need to regrout do I use sanded or
unsanded?

Thanks,