Blackroot Grey vs Signal Blue

How close are they?

ΔE 8.5, close: similar, with a visible difference side by side. Signal Blue is a little darker, more saturated than Blackroot Grey.

Can I use Signal Blue instead of Blackroot Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Signal Blue is a little darker, more saturated than Blackroot Grey.

Can I use Blackroot Grey instead of Signal Blue?

The same difference applies the other way round: Blackroot Grey is a little lighter, 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.