Fenrisian Grey vs Granite Stone

How close are they?

ΔE 20.5, loose: different enough that you should pick on purpose. Granite Stone is a little lighter, more muted than Fenrisian Grey.

Can I use Granite Stone instead of Fenrisian Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Granite Stone is a little lighter, more muted than Fenrisian Grey.

Can I use Fenrisian Grey instead of Granite Stone?

The same difference applies the other way round: Fenrisian Grey is a little darker, more saturated.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.