I don't know about the new GameMaker version, but in the old ones, the elaborate way to do the "flash" on hit was to write a shader for it, but that can be a nightmare in and of itself. The simpler but brute force method is probably to add a damaged animation or create a second object on top to create the flashing effect. Good luck!
Viewing post in [Devlog] "MOBILE CUTE BUNDAM" / Cute-'em-Up [SUBMITTED...??]
Using a sprite animation frame is a neat idea but awkward from the point of view of wanting the sprites possibly to animate in the future. Shaders seem to be the "simplest" way of doing it but this would also require me to learn OpenGL's own scripting language and uh...
yeah that is...that is a challenge I am entirely unprepared for. I am definately having a second object on top that's solid white but getting it to actually flash on and off correctly is being nightmarish at the moment. ^^;