fix color issue

when playersettings.colorspace is linear, the editor window color is wrong (still srgb). we should add logics to shader to fix this issue

com.unity.uiwidgets/Runtime/Resources/shaders/UIWidgets_GUITexture.shader

 Shader "UIWidgets/GUITexture"
 {
-    Properties { _MainTex ("Texture", any) = "" {} }
+    Properties { _MainTex ("Texture", any) = "" {} 
+                 _Linear ("_Linear", float) = 0
+    }
 
     CGINCLUDE
     #pragma vertex vert
     };
 
     sampler2D _MainTex;
+    
+    float _Linear;
 
     uniform float4 _MainTex_ST;
 
 
     fixed4 frag (v2f i) : SV_Target
     {
-        return 2.0f * tex2D(_MainTex, i.texcoord) * i.color;
+        fixed4 colr = 2.0f * tex2D(_MainTex, i.texcoord) * i.color;
+        float gamma = 2.2;
+        colr.rgb = _Linear ? pow(colr.rgb, (1.0/gamma)) : colr.rgb;
+        return colr;
     }
     ENDCG
 

com.unity.uiwidgets/Runtime/editor/surface.cs

 using System;
 using Unity.UIWidgets.foundation;
 using Unity.UIWidgets.ui;
+#if UNITY_EDITOR
+using UnityEditor;
+#endif
+
 using UnityEngine;
 using Canvas = Unity.UIWidgets.ui.Canvas;
 using Rect = UnityEngine.Rect;
 
             _guiTextureMat = new Material(guiTextureShader);
             _guiTextureMat.hideFlags = HideFlags.HideAndDontSave;
+#if UNITY_EDITOR
+            _guiTextureMat.SetFloat("_Linear", PlayerSettings.colorSpace == ColorSpace.Linear ? 1 : 0);
+#endif
             return _guiTextureMat;
         }