Thanks for the recommendation. I tried it out as a colorblind person. I'm always looking for one of two things -- tools that will help me differentiate stuff I see on graphs and charts (endlessly frustrating) and tools that will let me show other people how I see.
My problem is that I've never found a colorblind emulator that matches my colorblindness. I'm just red-green deficient, so nothing exotic.
My test for these emulators is whether I see a difference between the original unmodified image and the emulated colorblind image, and I always do. Even with this one. So that tells me that the emulation doesn't really match what I personally see or I wouldn't be able to tell the difference.
I haven't used sim daltonism, but most of these simulators assume your opsins are fully non-functional. You usually have multiple copies of the relevant genes and most of them need to be non-functional for complete colorblindness. Most people are only partially colorblind as a result, from what I understand.
Additionally, mutations can shift your spectral sensitivity curves away from "human normal", which further affects color perception.