Do Pinstripes change colors??

Since around 3 month my pinstripe is getting more yellow in certain areas, he was fully brown when i got him a year ago...
Is it something normal?did he catch a kind of scale disease??He's healthy and never refused a rat...

http://farm4.staticflickr.com/3679/9...7bd8b0f5_b.jpg

http://farm6.staticflickr.com/5490/9...4a08763d_b.jpg

I don't know but am interested cause pinstripe is my fav morph! Very pretty snake by the way!!