示例

Shader "Custom/ColorMaskTest"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
		//_ColorMask ABGR(1-2-4-8)
		//0表示不写入颜色通道到颜色缓冲区
		_ColorMask ("Color Mask", Float) = 15
		[Enum(UnityEngine.Rendering.CompareFunction)] _ZTest("ZTest", Float) = 4
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		//Cull Off
        //Lighting Off
        //ZWrite Off
        //Blend SrcAlpha OneMinusSrcAlpha
		ZTest [_ZTest]
		//向颜色缓冲区写入颜色通道值(0: 不写入)
		//ColorMask RGBA
        ColorMask [_ColorMask]

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			// make fog work
			#pragma multi_compile_fog
			
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				UNITY_FOG_COORDS(1)
				float4 vertex : SV_POSITION;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;
			
			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				UNITY_TRANSFER_FOG(o,o.vertex);
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				// sample the texture
				fixed4 col = tex2D(_MainTex, i.uv);
				// apply fog
				UNITY_APPLY_FOG(i.fogCoord, col);
				return col;
			}
			ENDCG
		}
	}
}

效果