Matt White vs Ivory Tusk

How close are they?

ΔE 21.7, loose: different enough that you should pick on purpose. Ivory Tusk is noticeably darker, more saturated than Matt White.

Can I use Ivory Tusk instead of Matt White?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Ivory Tusk is noticeably darker, more saturated than Matt White.

Can I use Matt White instead of Ivory Tusk?

The same difference applies the other way round: Matt White is noticeably 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.