One color creeper vision shader

I'm trying to change the creeper vision shader so that the entire screen will be a specific color (let's say white). This is what i have so far:
resourcepack\assets\minecraft\shaders\post\creeper.json
{
  "targets": [],
  "passes": [
    {
      "name": "creeper_bg",
      "intarget": "minecraft:main",
      "outtarget": "minecraft:main"
    }
  ]
}

resourcepack\assets\minecraft\shaders\program\creeper_bg.json
{
   "blend": {
       "func": "add",
       "srcrgb": "one",
       "dstrgb": "zero"
    },
   "vertex": "sobel",
   "fragment": "creeper_bg",
   "attributes": [],
   "samplers": [
      { "name": "DiffuseSampler" }
   ],
   "uniforms": []
}

resourcepack\assets\minecraft\shaders\program\creeper_bg.fsh
#version 150

out vec4 fragColor;

void main(){
  fragColor = vec4(1, 1, 1, 1);
}

From my understanding, this should make a white screen, but the screen is actually entirely black. How do I make it actually show the color that I want?