Polished Silver vs Mythril Blade

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Mythril Blade is a little lighter than Polished Silver.

Can I use Mythril Blade instead of Polished Silver?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Mythril Blade is a little lighter than Polished Silver.

Can I use Polished Silver instead of Mythril Blade?

The same difference applies the other way round: Polished Silver is a little darker.

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.