Mithril vs Platinum Crown

How close are they?

ΔE 23.4, loose: different enough that you should pick on purpose. Platinum Crown is noticeably lighter, more saturated than Mithril.

Can I use Platinum Crown instead of Mithril?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Platinum Crown is noticeably lighter, more saturated than Mithril.

Can I use Mithril instead of Platinum Crown?

The same difference applies the other way round: Mithril 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.