Gothic Blue vs Cygnar Blue Highlight

How close are they?

ΔE 25.5, loose: different enough that you should pick on purpose. Cygnar Blue Highlight is noticeably lighter, more saturated, cooler than Gothic Blue.

Can I use Cygnar Blue Highlight instead of Gothic Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Cygnar Blue Highlight is noticeably lighter, more saturated, cooler than Gothic Blue.

Can I use Gothic Blue instead of Cygnar Blue Highlight?

The same difference applies the other way round: Gothic Blue is noticeably darker, 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.