Te one that is yellow probably has a spider's nest blocking the Venturi Valve on that burner. The Venturi Valve acts as an air intake valve, for mixing the right ratio of air to gas, when the burner is burning.
Remove that burner and you will see the Venturi Valve on the open end of the burner that faces the control panel. It may have 2 slots or on each side of the burner tube, covered by a screen. Brush the screen with and old tooth brush to clear them. Also, check all the burner ports for clogs and clear those with a sewing needle. But, do not enlarge the holes. While you're at it, it would be a good idea to remove and clean all the burners, as required Annual Maintenance.
To assist you in properly removing the burners, I have included a link the the Owner's Manual for your model grill, in case you have misplaced yours. You can download & print the manual for future reference.
http://help.weber.com/manuals/pdf_files_2011/Gas/Genesis%20SilverGoldPlatinum/OwnersGuides/Genesis_LP_OwnersGuide_Plus_55826_103005.pdfI hope that all the information I have provided will help you troubleshoot and solve the problem
Happy Grilling and thanks for choosing FixYa.