Thousand Sons Blue vs Mirage Blue

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Mirage Blue is a little darker, much more muted than Thousand Sons Blue.

Can I use Mirage Blue instead of Thousand Sons Blue?

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

Can I use Thousand Sons Blue instead of Mirage Blue?

The same difference applies the other way round: Thousand Sons Blue is a little lighter, much 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.