Figgy Pink vs Stonewall Grey

How close are they?

ΔE 19.0, loose: different enough that you should pick on purpose. Stonewall Grey is a little darker, much more muted than Figgy Pink.

Can I use Stonewall Grey instead of Figgy Pink?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Stonewall Grey is a little darker, much more muted than Figgy Pink.

Can I use Figgy Pink instead of Stonewall Grey?

The same difference applies the other way round: Figgy Pink is a little 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.