Hex #663739 or rgb(102,55,57) in RGB space is the tint of red. It has hue angle of 357.45 degrees, value = 40 and saturation = 46. #663739 can be obtained by mixing 4 colors: 2 drops of yellow, 4 drops of red, 5 drops of blue, 4 drops of black.
Nearest safe hex - #663333. Below you can see the block with #663739 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #663739 to the mixer and play with it.