Necron Compound vs Platinum Crown

How close are they?

ΔE 35.0, loose: different enough that you should pick on purpose. Platinum Crown is noticeably lighter, more saturated than Necron Compound.

Can I use Platinum Crown instead of Necron Compound?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 35). Platinum Crown is noticeably lighter, more saturated than Necron Compound.

Can I use Necron Compound instead of Platinum Crown?

The same difference applies the other way round: Necron Compound 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.