Phthalo Blue RS vs Dark Blue

How close are they?

ΔE 11.6, fair: the same colour family, but not a straight swap. Dark Blue is a little lighter, more muted, cooler than Phthalo Blue RS.

Can I use Dark Blue instead of Phthalo Blue RS?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Dark Blue is a little lighter, more muted, cooler than Phthalo Blue RS.

Can I use Phthalo Blue RS instead of Dark Blue?

The same difference applies the other way round: Phthalo Blue RS is a little darker, more saturated, 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.