Martian Ironearth vs Raw Umber

How close are they?

ΔE 17.6, loose: different enough that you should pick on purpose. Raw Umber is a little darker, much more muted than Martian Ironearth.

Can I use Raw Umber instead of Martian Ironearth?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Raw Umber is a little darker, much more muted than Martian Ironearth.

Can I use Martian Ironearth instead of Raw Umber?

The same difference applies the other way round: Martian Ironearth is a little 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.