Inner Light vs Sulfuric Yellow

How close are they?

ΔE 21.2, loose: different enough that you should pick on purpose. Sulfuric Yellow is much more saturated, cooler than Inner Light.

Can I use Sulfuric Yellow instead of Inner Light?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Sulfuric Yellow is much more saturated, cooler than Inner Light.

Can I use Inner Light instead of Sulfuric Yellow?

The same difference applies the other way round: Inner Light is much more muted, warmer.

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.