ΔE 16.7, loose: different enough that you should pick on purpose. Dark Mud is noticeably darker, more muted, warmer than Steel Helmet Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Dark Mud is noticeably darker, more muted, warmer than Steel Helmet Green.
The same difference applies the other way round: Steel Helmet Green is noticeably lighter, 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.
See Steel Helmet Green on the colour wheel See Dark Mud on the colour wheel
All matches: Steel Helmet Green equivalents · Dark Mud equivalents