Warpfiend Grey vs Faded Plum

How close are they?

ΔE 16.8, loose: different enough that you should pick on purpose. Faded Plum is noticeably lighter, more saturated, warmer than Warpfiend Grey.

Can I use Faded Plum instead of Warpfiend Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Faded Plum is noticeably lighter, more saturated, warmer than Warpfiend Grey.

Can I use Warpfiend Grey instead of Faded Plum?

The same difference applies the other way round: Warpfiend Grey is noticeably darker, more muted, cooler.

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.