DaltonPilot
See your scene as colour-blind viewers see it, live in the 3D viewport.
DaltonPilot adds a button to Blender’s 3D viewport header. You click it and the viewport shows deuteranopia, protanopia, tritanopia or achromatopsia. A split view puts the original and the simulation side by side.
Your F12 renders and your compositor stay untouched.