ΔE 12.6, fair: the same colour family, but not a straight swap. Mythic Turquoise is a little darker, more muted, warmer than Turquoise Siren.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Mythic Turquoise is a little darker, more muted, warmer than Turquoise Siren.
The same difference applies the other way round: Turquoise Siren is a little lighter, more saturated, 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.
See Turquoise Siren on the colour wheel See Mythic Turquoise on the colour wheel
All matches: Turquoise Siren equivalents · Mythic Turquoise equivalents