I am working on GUI for my game, but I think this question could apply to any object in general - How to clearly highlight object regardless of its color? Currently I am blending its result color with other semi-transparent color(light blue), but obviously - this does not work for blue objects.
What are my options if I would like an object highlighted? I am looking for OpenGL shader solutions, best in customizable ones (e.g. more variants/ intensities).