Thunderhawk Blue vs Paynes Gray

How close are they?

ΔE 17.7, loose: different enough that you should pick on purpose. Paynes Gray is noticeably darker, more muted than Thunderhawk Blue.

Can I use Paynes Gray instead of Thunderhawk Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Paynes Gray is noticeably darker, more muted than Thunderhawk Blue.

Can I use Thunderhawk Blue instead of Paynes Gray?

The same difference applies the other way round: Thunderhawk 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.