Speed Yellow vs Moss and Lichen

How close are they?

ΔE 26.5, loose: different enough that you should pick on purpose. Moss and Lichen is a little darker, much more muted, cooler than Speed Yellow.

Can I use Moss and Lichen instead of Speed Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Moss and Lichen is a little darker, much more muted, cooler than Speed Yellow.

Can I use Speed Yellow instead of Moss and Lichen?

The same difference applies the other way round: Speed Yellow is a little lighter, much more saturated, warmer.

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.