Apple - MacBook Pro display suddenly has a very faint warm/pink tint

I handed in my computer with the problem to an authorized service shop. At first they didn't recognize the error, but after some further convincing from my part they claim to have spoken with Apple about it.

Apparently, the problem with warm hue is a software bug introduced in one of most recent versions of MacOS High Sierra (spring 2018), and it afflicts various Mac models. They claim that Apple is aware of the problem, and a fix will applied in an upcoming MacOS patch.

Status: As of MacOS Mojave 10.14.6 (2019-09-11), Apple seems not to have applied a fix, as the problem persists.

It sounds like you have Night Shift on. It tints all of your screens colors to be easier on the eyes.

System Preferences > Displays > Night Shift > Schedule > Off

Try that and see what happens. If that's it, you might want to turn it back on and set a schedule that works better for you.