Squig Orange vs Light Brown

How close are they?

ΔE 16.9, loose: different enough that you should pick on purpose. Light Brown is noticeably darker, more muted, warmer than Squig Orange. They are different kinds of paint: Citadel Squig Orange is an opaque base/layer paint and Green Stuff World Light Brown is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.

Can I use Light Brown instead of Squig Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Light Brown is noticeably darker, more muted, warmer than Squig Orange. They are different kinds of paint.

Can I use Squig Orange instead of Light Brown?

The same difference applies the other way round: Squig Orange is noticeably lighter, more saturated, 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.