Griffon Blue vs Mirage Blue

How close are they?

ΔE 15.8, loose: different enough that you should pick on purpose. Mirage Blue is noticeably darker, more muted than Griffon Blue.

Can I use Mirage Blue instead of Griffon Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Mirage Blue is noticeably darker, more muted than Griffon Blue.

Can I use Griffon Blue instead of Mirage Blue?

The same difference applies the other way round: Griffon Blue is noticeably lighter, more saturated.

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.