Dark Red Tone vs Agrax Earthshade

How close are they?

ΔE 25.8, loose: different enough that you should pick on purpose. Agrax Earthshade is noticeably lighter, much more muted, warmer than Dark Red Tone.

Can I use Agrax Earthshade instead of Dark Red Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Agrax Earthshade is noticeably lighter, much more muted, warmer than Dark Red Tone.

Can I use Dark Red Tone instead of Agrax Earthshade?

The same difference applies the other way round: Dark Red Tone is noticeably darker, much more saturated, cooler.

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.