Ruinous Spell vs Cobalt Green

How close are they?

ΔE 8.9, close: similar, with a visible difference side by side. Cobalt Green is warmer than Ruinous Spell.

Can I use Cobalt Green instead of Ruinous Spell?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Cobalt Green is warmer than Ruinous Spell.

Can I use Ruinous Spell instead of Cobalt Green?

The same difference applies the other way round: Ruinous Spell is 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.