There were mentioned studies in the book "Influence: The Psychology of Persuasion" that mirrored what your parents experienced.
Long story short, a jeweler was trying to move some turquoise and told an assistant to sell them at half price while she was gone. The assistant accidentally doubled the price, but the stones still sold immediately.
Turns out there's a phenomenon where humans automatically associate price to quality. So getting charged more means we think we're getting better quality, regardless of the actual quality
Honestly, you don't even need to specify 'brown', regular diamonds would apply. DeBeers has some awesome marketing, diamonds are one of the least beautiful gemstones.
Beauty depends entirely on the cut. (If you haven't seen diamonds with "old european" cuts - late 19th century, essentially - you should. They are so much more beautiful than the sterile modern cut ones)
Why would they approve this project if they didn't feel this was sufficient?
Only thing I can think is that the demand is going to be strong or they're thinking it's a steal with the contractor buying it out and are willing to experiment.
I'm all for new transit solutions and I'm really interested in this one, picking this route in particular though is what's odd to me...
Long story short, a jeweler was trying to move some turquoise and told an assistant to sell them at half price while she was gone. The assistant accidentally doubled the price, but the stones still sold immediately.
Turns out there's a phenomenon where humans automatically associate price to quality. So getting charged more means we think we're getting better quality, regardless of the actual quality