Uniform Grey vs N6 Neutral Gray

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. N6 Neutral Gray is noticeably lighter, more muted than Uniform Grey.

Can I use N6 Neutral Gray instead of Uniform Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). N6 Neutral Gray is noticeably lighter, more muted than Uniform Grey.

Can I use Uniform Grey instead of N6 Neutral Gray?

The same difference applies the other way round: Uniform Grey is noticeably 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.