In 1e, and I believe in 3e, discharged ioun stones (such as the ones that absorbed spells) became grey. In 1e, they granted their owner 10 PSPs, to a maximum of 50 (i.e. 5 stones); 3.5, they held 1 PSP before they broke.
In 2e, Ioun stones didn’t have a specific psionic use that I can find (correct me if I’m wrong).
What if you used receptacle on one? How much would it be worth as a PSP receptacle? I mean, sure, it’s a dull grey stone, but it also floats around your head.
You got an official reference for them holding one PSP in 3.5e?
Because I’m a massive 3.5e nerd and I’ve never heard of that before.
I cannot cite a quote to back up this statement though:
I remember being told when I was younger that anything applicable to 1e that wasn’t specifically revised by 2e was still applicable.
Under that logic, since it (ioun stones and their interactions with psionics) wasn’t specifically addressed by the 2e RAW, that’s still a valid rule.
I also vaguely remember an article on Ioun Stones from Dragon magazine. I believe it might be mentioned in there but have no certainty about that at the moment.
I’m a librarian. Of course I have a reference. 
“Dull gray stones are useless for magic but still harbor just enough resonance that a psionic character can eke out 1 power point before the stone is gone forever.”
I don’t have easy access to the books to give you a page number, however.
To “1e rules that aren’t contradicted are valid”, I agree. However, I think that tends to function more at the table level… I could easily see a DM saying “Nope, we’re not doing that”.
Ah, yeah, I’ve never noticed that before - quite the buried info.
Yeah, it’s been there on page 160 of the 3.5 EPH all along. Page 122 of the 3.0 Psionics Handbook, for even longer.
I quote the books over the SRD because the SRD is often is missing critical information for rules purposes. (looks at the leadership feat)
I, on the other hand, don’t have any of the books, so the SRD it is.
You are welcome to ask if ever you need a book reference.