Hex #556578 or rgb(85,101,120) in RGB space is the tint of blue. It has hue angle of 212.57 degrees, value = 47 and saturation = 29. #556578 can be obtained by mixing 4 colors: 4 drops of magenta, 5 drops of blue, 5 drops of green, 1 drop of white.
Nearest safe hex - #666666. Below you can see the block with #556578 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #556578 to the mixer and play with it.