Yes, colour sealer can be applied manually by a number of methods, including some I've done with an old toothbrush. After it has had sufficient time to dry on the grout, the residue is cleaned off the actual tiles. Here's one I did a year or so ago. I made up a colour to match these bathroom tiles.
I think your right, thats why i said they dont put it on, only sell it
If i want to match the grout colour and not change it, is this a reasonably easy job? Whats a good product?