Hex #666739 or rgb(102,103,57) in RGB space is the tint of yellow. It has hue angle of 61.30 degrees, value = 40 and saturation = 45. #666739 can be obtained by mixing 4 colors: 5 drops of yellow, 1 drop of red, 5 drops of blue, 4 drops of black.
Nearest safe hex - #666633. Below you can see the block with #666739 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #666739 to the mixer and play with it.