Royal Robes vs Asurmen Blue

How close are they?

ΔE 7.4, close: similar, with a visible difference side by side. Asurmen Blue is a little darker, cooler than Royal Robes.

Can I use Asurmen Blue instead of Royal Robes?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Asurmen Blue is a little darker, cooler than Royal Robes.

Can I use Royal Robes instead of Asurmen Blue?

The same difference applies the other way round: Royal Robes is a little lighter, 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.