Grey Seer vs Rainy Grey

How close are they?

ΔE 15.4, loose: different enough that you should pick on purpose. Rainy Grey is noticeably darker, more muted than Grey Seer.

Can I use Rainy Grey instead of Grey Seer?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Rainy Grey is noticeably darker, more muted than Grey Seer.

Can I use Grey Seer instead of Rainy Grey?

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