Deep Azure vs Grey Teal

How close are they?

ΔE 21.2, loose: different enough that you should pick on purpose. Grey Teal is noticeably lighter, more muted, warmer than Deep Azure.

Can I use Grey Teal instead of Deep Azure?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Grey Teal is noticeably lighter, more muted, warmer than Deep Azure.

Can I use Deep Azure instead of Grey Teal?

The same difference applies the other way round: Deep Azure is noticeably darker, more saturated, 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.