For floors - mostly ceramic tiles...

It needs to be flexible as the tiles are sitting on Marmox which is slightly
flexible.

I'm sorted on the adhesive - Mapei Kerabond + Isolastic - I tried some, then
tried to break it up and it held together like a b*stard.

Another complication with the grout, which I don't fully appreciate yet is
I'd like something that's either available in various very basic colours,
or can have colour added. I suspect we will need some in a light beigy or a
very pale colour and some in a darker grey based on tile choices so far.

How does one go about this?

Ta

Tim