This is what I have used in three water dioramas and have not harmed any plastics at all
https://armorama.kitmaker.net//features/150As far as coloring - hmmmm - They do make a tint for it, It wasn't any color I was looking for so I didn't use it. I tried to use Ritt cloth die - it worked but gave me purple (which was not what I wanted) - I was looking for a redish muddy color. Nothing Ritt did wrong, just not my color.
yes you can get it all at Michaels.