Is there any way to track the original colour of an instrument, by using the serial number? The instrument in question is an P-bass from October 1965, with number 11 03 20.
I don't think there is although serial numbers should tell you if the neck is maple or rosewood and if it's fretless or not. On the two basses I've restored/am restoring I've found that the electronics cavities were not originally painted at all and that's how I determined they were both natural finish.
I've never read or heard anything indicating that Fender tracked the properties of instruments by serial number. It seems to have been a pretty random thing with them, just issuing numbers as they rolled off the line. As far as I can tell, the best indicators of original color on an instrument are paint residue in the neck pocket or the pickup cavities (if refinished), and color under the pickguard (if original color).
All right, you guys. Thanks! I'll check the cavities.