Inner Light vs Naples Yellow

How close are they?

ΔE 16.9, loose: different enough that you should pick on purpose. Naples Yellow is a little darker, more saturated, warmer than Inner Light.

Can I use Naples Yellow instead of Inner Light?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Naples Yellow is a little darker, more saturated, warmer than Inner Light.

Can I use Inner Light instead of Naples Yellow?

The same difference applies the other way round: Inner Light is a little lighter, 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.