ΔE 34.2, loose: different enough that you should pick on purpose. Aquamarine is noticeably darker, much more saturated than Underbelly Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 34). Aquamarine is noticeably darker, much more saturated than Underbelly Blue.
The same difference applies the other way round: Underbelly Blue is noticeably lighter, much more muted.
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.
See Underbelly Blue on the colour wheel See Aquamarine on the colour wheel
All matches: Underbelly Blue equivalents · Aquamarine equivalents