Yellow washed out?

[Keen4Kritters]

Hi Guys Im resonably new to photography and I was wondering if you could help me out. Im Using a Canon 500d with a 150mm Sigma Macro lens and a 580exII canon speedlite. I recently got the opportunity to photograph some really nice yellow Ridge Tailed Monitors (type of goanna). However ever time I would take a picture the yellow seemed to become really washed out becomming more of a cream colour and the small amounts of red between the scales really popped out. I tryed various settings on the camera and on the flash. I even tryed without the flash in the natural sun but maintained a similar problem. If anyone has any suggestions on how to fix this problem it would be greatly appreciated. Also if anyone could edit these photos to have less red and more a yellow and black theme that would be great (as can be seen to some degree in the photos there is a white stripe down the back but the yellow on the sides is just far more intense in person if anyone could fix that). Pics attached.






PS I also attached some pics I got when wetting down the lizards if anyone is interested, I know they arn't of the standard of other pics on here but I quite like them.



Regards In Advance.