Hex #558f80 or rgb(85,143,128) in RGB space is the tint of greenish cian. It has hue angle of 164.48 degrees, value = 56 and saturation = 41. #558f80 can be obtained by mixing 4 colors: 1 drop of yellow, 3 drops of cyan, 3 drops of white, 5 drops of black.
Nearest safe hex - #669999. Below you can see the block with #558f80 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #558f80 to the mixer and play with it.