Blue Base vs Andrea Blue

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Andrea Blue is a little lighter, more saturated, cooler than Blue Base.

Can I use Andrea Blue instead of Blue Base?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Andrea Blue is a little lighter, more saturated, cooler than Blue Base.

Can I use Blue Base instead of Andrea Blue?

The same difference applies the other way round: Blue Base is a little 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.