ΔE 8.3, close: similar, with a visible difference side by side. Medium Grey Blue is more muted, warmer than Mythic Turquoise.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Medium Grey Blue is more muted, warmer than Mythic Turquoise.
The same difference applies the other way round: Mythic Turquoise is 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 Mythic Turquoise on the colour wheel See Medium Grey Blue on the colour wheel
All matches: Mythic Turquoise equivalents · Medium Grey Blue equivalents