Why is ReadPixels on my RenderTexture creating a pure gray texture?

Hello, I am trying to create a RenderTexture of the image below to eventually create a Texture2D that can be used in an sprite atlas later. I have found various tutorials and have come up with the following code:

 private Texture2D CreateAtlasTexture(int textureSize)
 {
         RenderTexture renderTexture = new RenderTexture(textureSize, textureSize, 24);
         Texture2D atlasTexture = new Texture2D(textureSize, textureSize, TextureFormat.ARGB32, false);
                 
         RenderCamera.aspect = 1.0f;
         RenderCamera.targetTexture = renderTexture;
         RenderCamera.Render();
                 
         RenderTexture.active = renderTexture;
         atlasTexture.ReadPixels(new Rect(0.0f, 0.0f, textureSize, textureSize), 0, 0);
         RenderTexture.active = null;
         RenderCamera.targetTexture = null;
                 
         return atlasTexture;
  }

However, when I run this code, and the camera preview looks like the screenshot below, I get a Texture2D that is 100% gray. Can someone help identify why this might be happening?

[1]: /storage/temp/29431-screen+shot+2014-07-19+at+6.39.36+pm.png