Ironjawz Yellow vs Estus Yellow

How close are they?

ΔE 17.7, loose: different enough that you should pick on purpose. Estus Yellow is noticeably lighter, more muted than Ironjawz Yellow.

Can I use Estus Yellow instead of Ironjawz Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Estus Yellow is noticeably lighter, more muted than Ironjawz Yellow.

Can I use Ironjawz Yellow instead of Estus Yellow?

The same difference applies the other way round: Ironjawz Yellow is noticeably darker, 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.