Some hair coloras can cause some forms of skin cancer... But I think the joke is making fun of the fact that the girl killed herself accidently and the "Oops" is a pun meaning "She was a dumbass"
Oh I know it was about the sister dying and that, I was just wondering why the makers of that colour thing thought that colour was a mistake. I know it wasn't the main part of the picture, but I was just curious lol.