Phthalo Blue GS vs Royal Blue

How close are they?

ΔE 13.9, fair: the same colour family, but not a straight swap. Royal Blue is a little lighter, more muted, cooler than Phthalo Blue GS.

Can I use Royal Blue instead of Phthalo Blue GS?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Royal Blue is a little lighter, more muted, cooler than Phthalo Blue GS.

Can I use Phthalo Blue GS instead of Royal Blue?

The same difference applies the other way round: Phthalo Blue GS 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.