Trollblood Base vs Aquamarine

How close are they?

ΔE 24.2, loose: different enough that you should pick on purpose. Aquamarine is noticeably lighter, much more saturated, warmer than Trollblood Base.

Can I use Aquamarine instead of Trollblood Base?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Aquamarine is noticeably lighter, much more saturated, warmer than Trollblood Base.

Can I use Trollblood Base instead of Aquamarine?

The same difference applies the other way round: Trollblood Base is noticeably darker, much more muted, cooler.

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.