I've managed to implement pixel shaders properly in APRIL and I managed to get ARC's color modifier to run through the pixel shader. Now I just need to change a few things here and there in order to allow the tone modifier to be applied properly. I might be able to finalize this task even today.
EDIT: Done. There's just a weird bug where it won't work with Viewports properly, but I'll take a look at that another time.