Fulgurite Copper vs Overlord Brass

How close are they?

ΔE 18.0, loose: different enough that you should pick on purpose. Overlord Brass is noticeably lighter, much more saturated than Fulgurite Copper.

Can I use Overlord Brass instead of Fulgurite Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Overlord Brass is noticeably lighter, much more saturated than Fulgurite Copper.

Can I use Fulgurite Copper instead of Overlord Brass?

The same difference applies the other way round: Fulgurite Copper is noticeably darker, much 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.