Hex #556f71 or rgb(85,111,113) in RGB space is the tint of cyan. It has hue angle of 184.29 degrees, value = 44 and saturation = 25. #556f71 can be obtained by mixing 3 colors: 1 drop of cyan, 3 drops of white, 5 drops of black.
Nearest safe hex - #666666. Below you can see the block with #556f71 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #556f71 to the mixer and play with it.