Trollslayer Orange vs Orange Brown

How close are they?

ΔE 23.5, loose: different enough that you should pick on purpose. Orange Brown is noticeably darker, much more muted than Trollslayer Orange.

Can I use Orange Brown instead of Trollslayer Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Orange Brown is noticeably darker, much more muted than Trollslayer Orange.

Can I use Trollslayer Orange instead of Orange Brown?

The same difference applies the other way round: Trollslayer Orange is noticeably 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.