Palettes are available in different shapes and sizes and are made from a wide range of materials such as wood, acrylic, and disposable paper, etc.  There are alsol paint mixing trays and cups for watercolors.

Oil and acrylic paint can be used successfully on any palette surface.  Watercolors work best on palettes that have slanted wells, shallow dishes and / or mixing areas.  Oil paint can be easily removed with turpentine or scraped off with a blade.  The same holds true for acrylics and watercolors, although water should be used instead of turpentine.