The Yamaha parts list shows that number as the stock/standard spring, and describes the colors as Gold/White. It may no longer be available though unless it is already sitting on a shelf somewhere.
The alternate spring part# that they show is 90501-555A1-00, and still available.
A google search of 90501-523A4-00 fluked me a dealer in Nova Scotia with a NEW spring still in package!! Paid $30 cdn shipped, and it arrived last night!