Mechanicus Standard Grey vs Templar Blue

How close are they?

ΔE 7.6, close: similar, with a visible difference side by side. Templar Blue is more saturated than Mechanicus Standard Grey.

Can I use Templar Blue instead of Mechanicus Standard Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Templar Blue is more saturated than Mechanicus Standard Grey.

Can I use Mechanicus Standard Grey instead of Templar Blue?

The same difference applies the other way round: Mechanicus Standard Grey is more muted.

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.