Being an item on their 'bucket list', I'd presume your friends have performed at least a cursory level of due diligence on the subject?
The article at Geology.com reinforces the handful of things I previously knew about jade:
...that there are two kinds; jadeite & nephrite
...that most jadeite undergoes some level of treatment as a part of the normal manufacturing/refining process
It asserts that there is a large audience in HK for jadeite. I'll elaborate further that while the diamond industry dots the globe with diamond grading labs (GIA, EGL, etc), Hong Kong has (last I checked) the sole lab for grading and verifying jade.
In buying a pricey piece of Imperial Jade from the likes of Chow Tai Fook (et al) for upwards of 50,000hkd, I'd expect it to be accompanied by a verification certificate from the HK lab in the same way a high-end diamond over a carat should be paired with an EGL, GIA, or ISI certificate. Given the level of competition among the mega-shops, I'd expect this to factor into their decision to avoid color-enhanced low-grade fakes. Doing otherwise would dry their stream of wealthy mainlanders who clamor into HK to gobble up primo jade by the trayfull.
The flip side of this may be that their 'bucket list' intention is merely to go through the EXPERIENCE of completing the task in this geographic spot and not so much about the jade quality as the paramount goal. HK street vendors offering varying levels of treated jade are certainly plentiful. Find a piece that's pretty to you, haggle the hell out of it, and enjoy it for its brief aesthetic and nostalgic value. Over the next 5 years, if it cracks from brittleness or loses coloration, you won't have paid much. If it lasts well beyond that, bonus!