Hex #999000 or rgb(153,144,0) in RGB space is the tint of yellow. It has hue angle of 56.47 degrees, value = 60 and saturation = 100. #999000 can be obtained by mixing 3 colors: 3 drops of yellow, 3 drops of red, 4 drops of green.
Nearest safe hex - #999900. Below you can see the block with #999000 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #999000 to the mixer and play with it.