shader.m

        uniform vec3 c_colorToReplace;
        uniform float c_thresholdSensitivity;
        uniform float c_smoothing;

        #pragma transparent
        #pragma body

        vec3 textureColor = _surface.diffuse.rgb;

        float maskY = 0.2989 * c_colorToReplace.r + 0.5866 * c_colorToReplace.g + 0.1145 * c_colorToReplace.b;
        float maskCr = 0.7132 * (c_colorToReplace.r - maskY);
        float maskCb = 0.5647 * (c_colorToReplace.b - maskY);
        
        float Y = 0.2989 * textureColor.r + 0.5866 * textureColor.g + 0.1145 * textureColor.b;
        float Cr = 0.7132 * (textureColor.r - Y);
        float Cb = 0.5647 * (textureColor.b - Y);
        
        float blendValue = smoothstep(c_thresholdSensitivity, c_thresholdSensitivity + c_smoothing, distance(vec2(Cr, Cb), vec2(maskCr, maskCb)));
        
        float a = blendValue;
        _surface.transparent.a = a;