ΔE 14.8, fair: the same colour family, but not a straight swap. Pale Indigo is noticeably lighter, cooler than Indigo Sky.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Pale Indigo is noticeably lighter, cooler than Indigo Sky.
The same difference applies the other way round: Indigo Sky is noticeably darker, 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 Indigo Sky on the colour wheel See Pale Indigo on the colour wheel
All matches: Indigo Sky equivalents · Pale Indigo equivalents