Matt White vs Menoth White Highlight

How close are they?

ΔE 15.4, loose: different enough that you should pick on purpose. Menoth White Highlight is a little darker, much more saturated than Matt White.

Can I use Menoth White Highlight instead of Matt White?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Menoth White Highlight is a little darker, much more saturated than Matt White.

Can I use Matt White instead of Menoth White Highlight?

The same difference applies the other way round: Matt White is a little lighter, much 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.