I have an idea that I would like to read up on but, I'm not sure what the best path would be. First, I need to determine if there is a reasonably priced and safe material that can have its color changed when exposed to a low-level magnetic field. I would prefer a material where the color change would occur relatively quickly - on the order of a second or less. I'm also open to materials that change color under other conditions such as light, heat, etc. I'm not sure if I should look into various chemicals, nanotechnology, or what. Does anyone have any suggestions on what might be the best direction to look?