Hmm.. Interesting! I've never heard that before about black but I know you can get denim colour transfer with the oak. Mine is so far so good though. It got completely drenched yesterday because I got caught in heavy summer rain but it's still fine. I sprayed mine with Collonil though. Has your friend's friend done the same with hers?
No problems with colour tranfer either way (bag to clothes or clothes to bag) with my oak leopard or pink leopard alexas. i have worn them with light coloured clothes and with dark demims with no ill effects xx