ΔE 12.3, fair: the same colour family, but not a straight swap. Undead Dragon is a little darker, more saturated than Holy White.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Undead Dragon is a little darker, more saturated than Holy White.
The same difference applies the other way round: Holy 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 Holy White on the colour wheel See Undead Dragon on the colour wheel
All matches: Holy White equivalents · Undead Dragon equivalents