I had 3 attempts at getting a Mini with a good screen. First was washed out and very yellow (similar to what you were describing), second was better on both fronts but had an extremely severe off-axis color shift, third was like the first. All were returned.
Every time each Mini was compared directly to my iPad, iPhone X, my wife’s 11, or any MacBook screen it looked much worse. Ultimately, I couldn’t justify the cost for what amounted to a downgraded screen. A real shame, as the form factor was a huge upgrade for my usage.
Overall, it does not appear that anyone posting in this thread has shared evidence of a perfect Mini screen. It was enough to convince me to wait for the 13 and see what improvements are made.