The potential story concept I have needs a tattoo that can change colour. I was wondering how possible that might be given small advances in current technology. From research I've found the 'black light' tattoo that will appear only under certain light conditions and some articles where medical researchers were attempting to easily display a persons Glucose level by having a small indicator tattoo change colour. Not sure if this was achieved or not, the page only mentions the attempt.
The level of colour changing is also important. I'd rather go down the path of a black tribal style that can change shape by changing from black to transparent to alter the pattern or outline. Maybe by just tattooing a large area with small dots and then controlling the dots to be 'on' or 'off'. The other route of a more chameleon like multi colour active camouflage isn't really required for my concept.
Now I'm happy with small amounts of handwaving but I'd like it to be more plausible than 'magic tattoo ink'.
EDIT for clarity.
The change in shape/colour should be controllable by the person. I imagine it being something to do with mental state being able to control (or partially control) the body. Perhaps some form of meditation or mental state. I've read of people being able to control their own heart rate or people who undergo operations with no anesthetic as they can 'control' or 'ignore' the pain.
Now it may well be too far fetched even with handwaving to allow a person full control over all the dots to achieve any pattern they want all the time so maybe we have to default to a number of set patterns. So we end up with something like 'when calm or when using no thought' you have the default pattern but 'when angry or by using a small amount of concentration' you can change to a different pattern. I guess this would allow people with more control to have more available patterns to choose from so a master might seem to be able to change to anything they wanted just because they have a larger library of options.
On reflection using emotion is probably not a great idea because in general people can lose control of their emotions quite easily.