Invisibe ink that reflects specific light?

Question

Is there a cheap invisible/transparent ink that reflects only special kinds of light? And how does it do it?

What kind of light?

Answer 1

The most common invisible ink that reacts to certain kinds of light is starch in water, which is invisible against paper or cloth but glows blue/purple in UV light.    Milk as invisible ink becomes visible under gentle heat turning brown, but it stays brown, so it isn't just light.