Hex #558740 or rgb(85,135,64) in RGB space is the tint of grass green. It has hue angle of 102.25 degrees, value = 53 and saturation = 53. #558740 can be obtained by mixing 3 colors: 4 drops of red, 3 drops of cyan, 5 drops of green.
Nearest safe hex - #669933. Below you can see the block with #558740 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #558740 to the mixer and play with it.