Underground must be white. 
2 colors maximum. Black + Second color for the double oo 
2D logo (not 3D) 
The letters must be in black written (except the double oo) 
 
The main idea in this domain name, is that merchants want to promote their shops online, and affiliate promote products of these merchants. 
 
The double oo can be used to display an &quot;infinite&quot; icon, or be used for 2eyes, or simply display with a different color than the other letters. 
 
Keep it simple, clear, readable, and note that the double oo must be easy to remember.

Hi Bonet. Very good job. Your logo will be used on www.promootion.com . You were very professional. Thanks again. Maxime