ΔE 11.8, fair: the same colour family, but not a straight swap. Deep Sky Blue is a little lighter, more muted than Relic Blue.
✓ Two Thin Coats comparison chart lists these two as equivalents.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Deep Sky Blue is a little lighter, more muted than Relic Blue.
The same difference applies the other way round: Relic Blue is a little darker, more saturated.
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 Relic Blue on the colour wheel See Deep Sky Blue on the colour wheel
All matches: Relic Blue equivalents · Deep Sky Blue equivalents