
The dorsal stripe is quite common on westies sometimes more noticable when they are younger.
I have read so many reasons for it, so not quite 100% convinced one way or another yet. If your dog is healthy enough don't worry about it too much.
Sometimes it is more noticeable in a soft coat as the coat tends to look that bit whiter, sometimes a very harsh coat can have a slight wheaten appearance. Some lines are far more whiter than others.
One of my girls had it and at the time I was adviced to give evening primrose oil, which I did faithfully and it did go away through time but I never 100% knew if this is what made it go away or if it just got lighter as she got older.
Some people call it Orange stripe. It is not uncommon though.
Pam
PS there are a few westie folk on the board who have had the breed quite a while so maybe they could chip in..