varying float LightIntensity; 
varying vec3  MCposition;

uniform vec4 SkyColor;
uniform vec4 CloudColor;
uniform float Bias;
uniform sampler3D Noise3;

void main()
{
    vec4  noisevec  = texture3D( Noise3, MCposition );

    float intensity = ( noisevec[0] + noisevec[1] + noisevec[2] + noisevec[3] - 1. ) / 2.;

    vec3 color   = mix( SkyColor.rgb, CloudColor.rgb, clamp( Bias+intensity, 0., 1. ) ) * LightIntensity;

    gl_FragColor = vec4(color, 1.0);
}