dolphin/Data/User/Shaders/sepia.txt

uniform samplerRECT samp0 : register(s0);

void main(out float4 ocol0 : COLOR0, in float2 uv0 : TEXCOORD0)
{
  float4 c0 = texRECT(samp0, uv0).rgba;
  // Same coefficients as grayscale2 at this point
  float avg = (0.222 * c0.r) + (0.707 * c0.g) + (0.071 * c0.b);
  float red=avg;
  // Not sure about these coefficients, they just seem to produce the proper yellow
  float green=avg*.75;
  float blue=avg*.5;
  ocol0 = float4(red, green, blue, c0.a);
}