Mythril Blade vs Gold (Metallic)

How close are they?

ΔE 17.8, loose: different enough that you should pick on purpose. Gold (Metallic) is noticeably lighter, more saturated than Mythril Blade.

Can I use Gold (Metallic) instead of Mythril Blade?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Gold (Metallic) is noticeably lighter, more saturated than Mythril Blade.

Can I use Mythril Blade instead of Gold (Metallic)?

The same difference applies the other way round: Mythril Blade 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.