ΔE 20.5, loose: different enough that you should pick on purpose. Aquamarine is noticeably lighter, much more saturated, cooler than Mythic Turquoise.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Aquamarine is noticeably lighter, much more saturated, cooler than Mythic Turquoise.
The same difference applies the other way round: Mythic Turquoise is noticeably darker, much more muted, warmer.
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 Mythic Turquoise on the colour wheel See Aquamarine on the colour wheel
All matches: Mythic Turquoise equivalents · Aquamarine equivalents