(Pixelmator Pro 1.0.8 on macOS 10.13.3 on a MacBook (Retina, 12-inch, Early 2015))
I was doing some lettering earlier, taking the colour of each letter in a text object from an already existing image that I was using as a swatch. I've put a simulation of what I was doing in an image below. I'm having trouble with Pixelmator Pro's text eyedropper (2).
If I select a letter and click on the colour patch (1) the colour of the letter changes as I would expect.
If I select a letter and click on Pixelmator Pro's text eyedropper (2) the colour of the whole text changes instead of the letter as I was expecting.
If I select a letter and click on Apple's eyedropper (3) the colour of the letter changes as I would expect (so I can use this as a workaround).