[G6Tanuki]

"House codes" for transistors, and various colour-stripes, seem to have been widespread; yes we're all familiar with the colour-codes indicating gain on the likes of the 2N2926/3906 transistors, but I've got a bunch of the little "Jelly-bean" Fairchild transistors here [the ones with a dull brown ceramic bottom and a shiny brown domed Epoxy-topping] which have colour-smudges whose significance I have never heard explained.

I suspect that quite a few of these colour-blobs were internal manufacturing-things, if you had several production-lines whacking-out identical transistors, you'd have each line's output identified by colour-blobs, so when samples were sent to QA for testing they could identify which line any not-quite-up-to-spec parts were coming from.