Hello,
I purchased an item in the auction house for over 350,000 gold. I then went to the mailbox excited about my new purple diadem only to open it and find that it is green. I thought to myself that perhaps made a mistake and went back to the auction house to purchase a purple diadem that will match all my gear. I clicked on ctrl and the item to make sure it was purple and in the photo - it is purple. I bought the second one thinking I must have made a mistake with the first one. Then I went to the mail to collect my item and clicked on ctrl and the item again, and it is also green. I have now spent over 700,000 gold on this false portrayal of the item in the auction house. I would like a refund, or to be provided with the purple color that was shown as the item being purchased. I am so upset over this. Usually I don’t complain, but spending that much money should mean I get what was shown in the image on the auction. If you could please help me, that would be great. I worked hard to earn that much gold and feel I have been robbed.
Thank you,
Brenda
We generally aren’t able to assist with or refund items purchased through the Auction House, so I’m not sure what can be done. That said I’d recommend two things.
First, be sure to submit a bug report so that our QA team can take a look. Second, submit a ticket and ask. I can’t make any guarantees but if we can verify a bug there may be something that we can do.
Edit: It looks like you basically copy/paste what you wrote here into your ticket. I’d recommend including some actionable information. Like the character name and the exact names of the item you are referring to. There isn’t an item called a Purple or Green Diadem in the game. 
Perhaps you should show us the item in question.
I suspect there is more to this than meets the eye.
Just curious, which diadem was it that you were trying to purchase?
Was it the Diadem of the Highborne? I know that the Raid Finder version of that head piece is the purple version.
Link to set view: https://www.wowhead.com/transmog-set=2458/radiant-lightbringer-armor-raid-finder-recolor
LFR = Purple
Normal = Yellow
Heroic = Green
Mythic = Different model
Also, you can check out how an item on the AH will look on your toon by using Ctrl-Click.
From their OP, they were doing that. The issue is that the image was not matching up with the actual appearance once they had the item.
However, I am not sure if they were doing the preview from the icon at the top of the listings OR if they were checking each individual listing before they purchased the item.
I’ve ran into this situation as well, with the leather belt(monk set) boe from Tomb of Sargeras.
I’m not sure what causes it, but items with varying colors(such as these), seem to have a habit of only showing up as X color in the preview window. The same thing can also happen with certain pets(such as the Octopode Fry or whatever its called from Islands).
Again though, no clue what causes it, as it is inconsistent. But I definitely get the OP’s frustration. So I can’t help but offer my support and wish them luck.
3 years later, and this is still happening with countless items on the AH.
I was told by a GM that this is “working as intended.”
No joke. It’s not a bug. It’s an intentional feature.
You already acknowledged the time frame, please don’t necro old posts. I can guarantee that something has changed in the interim.
When buying items on the AH, make sure you are hovering over the actual item in question when you get to the different listings.