NEWS - Apple says tattoos can cause problems with the Apple Watch
Apple has recently expressed how wearing there new smart watch over tattoos can affect the watch's functions, Dark colored tattoos can fool The light sensor's at the back of the watch which can cause the watch not to work correctly.
"Permanent or temporary changes to your skin, such as some tattoos can impact heart rate sensor performance" As stated on a support page on apples website. "The ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings." This means that if you have tattoos where the watch would be you should make sure the watch works correctly before purchasing.
But hopefully this issue will be resolved.