I can remember when I was a child, getting Epsom salts and adding colours to it to make different coloured bath salts to friends for Christmas presents. I'm sorry that I'm not 100% certain about what the colouring agent was, but I think it was food colouring. If you give it a try, I hope it works out.
Have a Great Day!! :)
Fun to do!
Relaxing as well what a great ideat & great puzzle!
Thanks Staff!