Deep Grey vs Faded Purple

How close are they?

ΔE 19.6, loose: different enough that you should pick on purpose. Faded Purple is noticeably lighter, more saturated, warmer than Deep Grey.

Can I use Faded Purple instead of Deep Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Faded Purple is noticeably lighter, more saturated, warmer than Deep Grey.

Can I use Deep Grey instead of Faded Purple?

The same difference applies the other way round: Deep Grey is noticeably darker, more muted, 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.