Are there any specific questions you want answered after reading the explanation on their website?

If you book an itinerary that has you staying for a night (or more) at Doha, then you will obviously have a blue-edged boarding pass (as Doha is your final destination for that day's travel). You surely wouldn't expect them to force you to wait at the airport for a connecting flight that doesn't depart until the following day, or even later!!!

All Economy passengers travel on the same bus, regardless of whether they are transferring or terminating at DOH. The colour coding is more for allowing ground staff to instantly recognise your particular circumstance (as a Premium, Transfer, Terminating pax) without having to ask. You're likely to be intercepted if you flash your boarding wallet while going through the unintended channel, but there's nothing to stop you from going the yellow route if you have a blue boarding wallet, or vice versa.