Tidal Wave vs Celestium Blue

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. Celestium Blue is noticeably darker, warmer than Tidal Wave.

Can I use Celestium Blue instead of Tidal Wave?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Celestium Blue is noticeably darker, warmer than Tidal Wave.

Can I use Tidal Wave instead of Celestium Blue?

The same difference applies the other way round: Tidal Wave is noticeably lighter, 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.