Crusader Skin vs Bright Slate Grey

How close are they?

ΔE 41.0, loose: different enough that you should pick on purpose. Bright Slate Grey is noticeably darker, much more muted than Crusader Skin.

Can I use Bright Slate Grey instead of Crusader Skin?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 41). Bright Slate Grey is noticeably darker, much more muted than Crusader Skin.

Can I use Crusader Skin instead of Bright Slate Grey?

The same difference applies the other way round: Crusader Skin is noticeably lighter, much more saturated.

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.