Hex #660000 or rgb(102,0,0) in RGB space is the tint of red. It has hue angle of 0.00 degrees, value = 40 and saturation = 100. #660000 can be obtained by mixing 2 colors: 2 drops of red, 3 drops of black.
Nearest safe hex - #660000. Below you can see the block with #660000 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #660000 to the mixer and play with it.