Basilicanum Grey vs Spectral Wolf

How close are they?

ΔE 21.6, loose: different enough that you should pick on purpose. Spectral Wolf is noticeably lighter, more saturated than Basilicanum Grey.

Can I use Spectral Wolf instead of Basilicanum Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Spectral Wolf is noticeably lighter, more saturated than Basilicanum Grey.

Can I use Basilicanum Grey instead of Spectral Wolf?

The same difference applies the other way round: Basilicanum Grey is noticeably darker, 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.