主要思路通过RT截图，拷贝到一个Texture2D 上，新建一个材质球用Unlit_YellowFilterShader，改变_GrayAmount参数达到效果

//屏幕截图泛黄滤镜
    public static void SetTextureShotFilter(Transform tf_, float duration_, LuaFunction func_)
    {
        Camera camera = CameraMgr.Instance.MainCamera;     
        float current_width = UIHelper.GetNGUIScreenWidth();
        float current_height = UIHelper.GetNGUIScreenHeight();
        UnityEngine.Rect rect = new Rect(current_width * 0f, current_height * 0f, current_width * 1f, current_height * 1f);
        // 创建一个RenderTexture对象  
        RenderTexture rt = new RenderTexture((int)rect.width, (int)rect.height, 16);
        // 临时设置相关相机的targetTexture为rt, 并手动渲染相关相机  
        camera.targetTexture = rt;
        camera.Render();
        // 激活这个rt, 并从中中读取像素。  
        RenderTexture.active = rt;
        Texture2D screenShot = new Texture2D((int)rect.width, (int)rect.height, TextureFormat.RGBA32, false);
        screenShot.ReadPixels(rect, 0, 0);// 注：这个时候，它是从RenderTexture.active中读取像素  
        screenShot.Apply();
        // 重置相关参数，以使用camera继续在屏幕上显示  
        camera.targetTexture = null;
        //ps: camera2.targetTexture = null;  
        RenderTexture.active = null; // JC: added to avoid errors  
        GameObject.Destroy(rt);
        OperaMgr.Instance.CreateYellowFilter(tf_, screenShot, duration_, () =>
        {
            if (func_ != null)
            {
                func_.Call();
            }
        });
    }

Shader代码：

Shader "Ygame/Unlit/Unlit_YellowFilter"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _GrayAmount("GrayAmount", Range(-2.0, 3.0)) = 0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        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;
                fixed4 color : COLOR;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                fixed4 color : COLOR;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float _GrayAmount;

            
            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) : COLOR
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                float grey = dot(col.rgb, float3(0.299, 0.587, 0.114));
                col.rgb = lerp(col.rgb, float3(grey, grey, grey), _GrayAmount);
                float3 filter = lerp(float3(1,1,1), float3(251.0 / 256, 220.0 / 256, 189.0 / 256), _GrayAmount);
                col.rgb = (col.rgb * filter);
                return col;
            }
            ENDCG
        }
    }
}