Fluor White vs Moss and Lichen

How close are they?

ΔE 70.7, loose: different enough that you should pick on purpose. Moss and Lichen is noticeably darker, much more saturated than Fluor White.

Can I use Moss and Lichen instead of Fluor White?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 71). Moss and Lichen is noticeably darker, much more saturated than Fluor White.

Can I use Fluor White instead of Moss and Lichen?

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