What do these transistor color bar markings mean?

Hi
I visited my local Dick Smiths store today to buy a few transistors, when I noticed that they were getting rid of PN4258 transistors for 1 cent each. I didn't know what their specs were, but I figured that at 1 cent I couldn't go wrong - so I bought the whole stock, all 70 of them.

About half of the transistors have three color bars marked on their rounded surfaces of the TO92 package - red, silver, blue or white, brown , blue, or etc, etc.

I have never seen this before on any transistor, and the Fairchild data sheet does not mention it. What does it mean, please?

Thanks,
Andre

Could be a proprietary method a company used to come up with matching transistors?

Maybe... but some are marked and some are not, which is also odd.

I've always presumed it's a mark of gain groupings?, but I've never seen any info about it.

I suspect you are right about the gain groupings. Anyway, my needs are simple and gain is not important - I am using them to drive multiplexed 7-segment displays.