Khador Red Highlight vs Orange

How close are they?

ΔE 28.8, loose: different enough that you should pick on purpose. Orange is noticeably darker, more saturated, cooler than Khador Red Highlight.

Can I use Orange instead of Khador Red Highlight?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Orange is noticeably darker, more saturated, cooler than Khador Red Highlight.

Can I use Khador Red Highlight instead of Orange?

The same difference applies the other way round: Khador Red Highlight is noticeably lighter, 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.