Here's an abstract from the on-line help for GetCtrlAttribute (Attribute: Text Background Color):
Description: The RGB color value of the text background. ...
RGB value is a 4-byte integer with the hexadecimal format 0x00RRGGBB, with the respective red, green, and blue components. See MakeColor().
In your example: 16777011 = 0xFFFF33, that is Red = 255, Green = 255, Blue = 51, which gives yellow
Hope this helps
Roberto