Strong Grey vs Regiment Grey

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Regiment Grey is a little darker, more muted than Strong Grey.

Can I use Regiment Grey instead of Strong Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Regiment Grey is a little darker, more muted than Strong Grey.

Can I use Strong Grey instead of Regiment Grey?

The same difference applies the other way round: Strong Grey is a little 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.