I have some fluorescent red dye tablets I scarfed from a trashcan at GE years ago. Used for stream tracing. I looked on the internet once and found dye markers that divers use so you should be able to find them at a dive shop. The tablets I have do leave a temporary stain on the liner that goes away within an hour or so. You use so little of any dye there should be nothing to worry about.
Al

PS: Also welcome to the forum.