According to many professionals, retro bathroom tile designs ideas are very important to the whole interior bathroom look. With chosen tiles though you should avoid making straight and obviously clear lines. The designers offers such ideas as using soft curvatures. So, the circles may be of different diameters or they may be connected between themselves like being place one over another. There are many pictures and photos of such tiles and lines but you may rely on your own fantasy, too.
As for the colour of the tiles – you may forget about dark colours and leave them for the Gothic and Victorian style bathrooms. The only exception can be done to use dark colours as additional paintings on the light background. For example, the light beige wall tiles will be great background for the dark brown painting or elements. But it is worth to remember that paintings and background should be of the same colour scheme.