Color Space Conversion Issue in Custom Shader

I've examined your issue with the color corruption when using the #include <colorspace_fragment> in your custom shader. This is a common problem when working with partially transparent textures and color space conversions.

The Problem

The issue occurs because the color space conversion is being applied after your blending operation, but the blending itself should be performed in linear space with pre-multiplied alpha. When you include the colorspace_fragment chunk, it's converting your final blended result from linear to sRGB, but the blending math itself might not be properly accounting for the color space.

Solution

Here's how to fix this issue:

1. Make sure your textures are properly set up for the correct color space
2. Perform blending in linear space
3. Apply the color space conversion only to the final result

Try modifying your fragment shader like this:

GLSLCopied
void main() {
  // Sample both textures
  vec4 baseColor = texture2D(baseTexture, vUv);
  vec4 overlayColor = texture2D(overlayTexture, vUv);
  
  // Ensure both textures are in linear space for blending
  // If your textures are already in linear space, you can skip this step
  
  // Pre-multiply alpha for the overlay texture
  overlayColor.rgb *= overlayColor.a;
  
  // Perform the "over" blending operation in linear space
  vec4 finalColor = overlayColor + baseColor * (1.0 - overlayColor.a);
  
  // Now apply the color space conversion to the final result
  gl_FragColor = finalColor;
  
  // Include the color space conversion
  #include <colorspace_fragment>
}

The key is to ensure that:

1. Your blending math is correct for pre-multiplied alpha
2. The blending is performed in linear space
3. The color space conversion is applied only once at the end

You might also need to check the outputColorSpace property of your renderer, which should be set to THREE.SRGBColorSpace (the default) for proper conversion.

If you're still experiencing issues, you might need to manually implement the linear-to-sRGB conversion instead of using the built-in chunk, giving you more control over exactly how and when the conversion is applied.