Welcome to the Do-It forums Milcalcale!
Lots of people use worm salt while others simply use salts with very fine grains. I've heard of people putting salt in blenders and really turning it to dust, but be it salt or the Do-It HD additive, you'll see some opaquing and maybe even some color changing. Greying is a regular beef. Others will chime in here that use glass bead media for weighting plastic and that stuff is pretty transparent and may not mess with color too much. Personally I don't add anything to plastic to make it sink but there are guys here that do who will help you out.
Again, welcome aboard!