Paratrooper Tan vs Granite Grey

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Granite Grey is a little darker, more muted than Paratrooper Tan.

Can I use Granite Grey instead of Paratrooper Tan?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Granite Grey is a little darker, more muted than Paratrooper Tan.

Can I use Paratrooper Tan instead of Granite Grey?

The same difference applies the other way round: Paratrooper Tan is a little lighter, 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.