For one of my games I need to have a toon shader that works in both black and white and color. This is what I created for the black and white one:

here's the script:
Code:

---

 material mat_bw 
{	
	effect = "		
	sampler2D g_samSrcColor;

	float4 MyShader( float2 Tex : TEXCOORD0 ) : COLOR0
	{
		float4 Color;
		int Color_all;
		Color = tex2D( g_samSrcColor, Tex.xy);
		Color.rgb = (Color.r + Color.g + Color.b)/3;
		Color_all = (Color.r/.167);
		Color.rgb = Color_all * .167;
		return Color;
	}


	technique PostProcess
	{
		pass p1
		{
			VertexShader = null;
			PixelShader = compile ps_2_0 MyShader();
		}

	}
	";
} 

---

Now, the problem comes when I try to use the same kind of thing with color. I can't find a formula that would force the saturation to be a certain level. Any suggestions?