ΔE 12.2, fair: the same colour family, but not a straight swap. Ivory Tusk is a little darker, more muted than Howling Sand. They are different kinds of paint: Army Painter Howling Sand is a one-coat contrast-style paint and Two Thin Coats Ivory Tusk is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Ivory Tusk is a little darker, more muted than Howling Sand. They are different kinds of paint.
The same difference applies the other way round: Howling Sand is a little lighter, 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 Howling Sand on the colour wheel See Ivory Tusk on the colour wheel
All matches: Howling Sand equivalents · Ivory Tusk equivalents