Cygnar Blue Highlight vs Imperial Purple

How close are they?

ΔE 38.0, loose: different enough that you should pick on purpose. Imperial Purple is a little darker, much more saturated, warmer than Cygnar Blue Highlight.

Can I use Imperial Purple instead of Cygnar Blue Highlight?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 38). Imperial Purple is a little darker, much more saturated, warmer than Cygnar Blue Highlight.

Can I use Cygnar Blue Highlight instead of Imperial Purple?

The same difference applies the other way round: Cygnar Blue Highlight is a little lighter, much more muted, 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.