Its hard to say without seeing a picture and a seriel number. To my knowlege we never offered yellow as a color option. It is possible that we made a one-off in yellow at some point.
I used to own a mustard-yellow SR5, I had it professionally refinished to that color, but it was originally trans teal. I sold it to funkycarnivore, and he just recently sold it off again on Ebay. Nice bass, but that sucker was the HEAVIEST of the 4 SR5's that I've owned - also the best sounding, incidentally.