They changed to black for the 2013 model year but ONLY for the blue bike, the matt grey one retained the grey panels. From MY2014 onwards they all have black panels, even the matt grey bike! So you've got to be a bit savvy.
Here are the parts numbers:
Black LH: 11D-E240J-10
Black RH: 11D-E240K-10
Grey LH: 11D-E240J-00
Grey RH: 11D-E240K-00
Only place you'll get them is from a Yamaha dealer, or from AJ Sutton as mentioned. They set you back the best part of �120 for the pair! Lucky Craig might be able to help you out.
Here's a link to the black coloured panels at Suttons:
www.yamahamotorcyclespares.co.uk/genuineparts/26241/
Here's a handy link for anyone who wants/needs to know the available colours by year of all XTZ models:
http://www.yamaha-motor.eu/designcafe/en/about-bikes/off-road/index.aspx?view=article&id=599261&segment=Off%20Ro ad&archive=false&page=1