ΔE 24.1, loose: different enough that you should pick on purpose. Relic Blue is noticeably lighter, much more muted, cooler than Calth Blue Clear.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Relic Blue is noticeably lighter, much more muted, cooler than Calth Blue Clear.
The same difference applies the other way round: Calth Blue Clear is noticeably darker, much 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.
See Calth Blue Clear on the colour wheel See Relic Blue on the colour wheel
All matches: Calth Blue Clear equivalents · Relic Blue equivalents