Webbing Green vs Raw Umber

How close are they?

ΔE 16.5, loose: different enough that you should pick on purpose. Raw Umber is noticeably darker, much more muted than Webbing Green.

Can I use Raw Umber instead of Webbing Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Raw Umber is noticeably darker, much more muted than Webbing Green.

Can I use Webbing Green instead of Raw Umber?

The same difference applies the other way round: Webbing Green is noticeably lighter, much 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.