If don't like the colour of your ceramic bathroom tiles, there are a number ways to remedy the situation. Solutions include painting the tiles, refinishing the tiles with an acrylic coating and layering new tiles over the existing tiles. What you can't do is re-glaze the tiles, since tiles are glazed at very high temperatures in a special oven called a kiln.
Painting tiles requires basic painting and home repair skills. Before painting, remove and replace any loose grout between the tiles. Surface imperfections will be magnified after the paint is applied, so thoroughly clean the tiles and allow to dry. Sand the tiles with 220-grit carbide sandpaper or a muriatic acid-based deglosser. This will help the paint adhere to the tiles.
You can use either primer and an oil-based paint, or a two-part epoxy-based paint that is specially formulated for tiles. The advantage of oil-based paint is that it comes in a great variety of colours. The disadvantage is that it can't be applied to areas with heavy water exposure, such as tiled sinks and tubs. For maximum durability, the two-part epoxy-based paint is a better choice. Color tints for these paints are available, but limited to pastel shades. Epoxy-based paints come in brush-on and spray-on formulas. For the smoothest surface application, use a spray-on formula.
When applying the paint, you can either paint over the grout (the easiest choice), or carefully mask the grout with an acrylic masking tape formulated not to stick to paint.
This option is best left to contractors who specialise in acrylic refinishing for bathrooms and kitchens. It is a less expensive solution than removing and replacing the original tiles. The process involves thoroughly cleaning the tiles, applying a spray-on primer, applying several coats of a proprietary acrylic formula, then buffing the surface so that it resembles glazed tile. Acrylic refinishing is available in a wide variety of colours and textures that mimic real tile. Non-tiled bathroom surfaces, such as tubs and sinks, can also be treated this way. Confirm with the acrylic refinishing contractor that the product has a warranty, and is guaranteed to last a good number of years.
Another option is to layer new tile over your existing tiles. This can be done on tile floors and tile counter tops. It can be accomplished by someone experienced with tile installation, but the job is more complicated that installing tiles on an uncovered surface. If your existing tiled surface isn't perfectly flat, you will have to first even it out before installing the new tiles. Do this by applying an extra coat of epoxy mortar and a layer of backer board over the tiles before proceeding. Another consideration is that the new layer of tiles will raise the height of the tiled surface and you might have to make some adjustments to the door trim, doorways and bathroom fixtures to compensate.