Hex #66d54d or rgb(102,213,77) in RGB space is the tint of grass green. It has hue angle of 108.97 degrees, value = 84 and saturation = 64. #66d54d can be obtained by mixing 4 colors: 2 drops of yellow, 1 drop of cyan, 5 drops of green, 2 drops of white.
Nearest safe hex - #66cc66. Below you can see the block with #66d54d color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #66d54d to the mixer and play with it.