You will need to use a 2-part epoxy paint. Many can be applied directly to the tile without a primer but preparation is very important. The tile must be super clean and sanded with 180-220 grit sandpaper first.
Check with your local paint store for a good epoxy paint and its requirements for application to tile.
The use of regular primer and paint will not take the environment of a shower for very long before peeling. Only an epoxy can do this.