I had awful splashback tiles in my kitchen, they were brown and very unsightly. i couldnt afford to replace them for a while so i tried the tile paint in white. It wasn't a bad job, they were shiny and bright but it is not a long lasting finish. I managed to replace the kitchen 12 months later and the paint was beginning to flake off!!!
If it is just a temporary thing then Id say go for it but if you aret thinking of a permanent change I would save up and have them replaced.