Archangel Red vs Khador Red Highlight

How close are they?

ΔE 33.7, loose: different enough that you should pick on purpose. Khador Red Highlight is noticeably lighter, much more muted, warmer than Archangel Red.

Can I use Khador Red Highlight instead of Archangel Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 34). Khador Red Highlight is noticeably lighter, much more muted, warmer than Archangel Red.

Can I use Archangel Red instead of Khador Red Highlight?

The same difference applies the other way round: Archangel Red is noticeably darker, much 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.