Algae Green vs Garaghak's Sewer

How close are they?

ΔE 17.7, loose: different enough that you should pick on purpose. Garaghak's Sewer is noticeably darker, more muted than Algae Green.

Can I use Garaghak's Sewer instead of Algae Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Garaghak's Sewer is noticeably darker, more muted than Algae Green.

Can I use Algae Green instead of Garaghak's Sewer?

The same difference applies the other way round: Algae Green 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.