Hex #558939 or rgb(85,137,57) in RGB space is the tint of grass green. It has hue angle of 99.00 degrees, value = 54 and saturation = 58. #558939 can be obtained by mixing 4 colors: 1 drop of red, 4 drops of green, 2 drops of white, 2 drops of black.
Nearest safe hex - #669933. Below you can see the block with #558939 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #558939 to the mixer and play with it.