ΔE 10.1, fair: the same colour family, but not a straight swap. Skyshard is a little darker, more saturated than Washable White.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Skyshard is a little darker, more saturated than Washable White.
The same difference applies the other way round: Washable White is a little lighter, more muted.
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 Washable White on the colour wheel See Skyshard on the colour wheel
All matches: Washable White equivalents · Skyshard equivalents