There is no simple formula for #757573, but we have one for color #808079, that is similar to #757573 by 98%.
Color #808079 name: grayish yellow
Hex #808079 or rgb(128,128,121) in RGB space is the tint of yellow. It has hue angle of 60.00 degrees, value = 50 and saturation = 5. #808079 can be obtained by mixing 4 colors: 4 drops of yellow, 2 drops of magenta, 5 drops of blue, 1 drop of cyan.
Nearest safe hex - #999966. Below you can see the block with #808079 color and its structure: in procentage ratio and in drops of pigments. Click "TRY" button to move #808079 to the mixer and play with it.