Eyedropper not working in three-way color corrector Premiere Elements

am I doing something wrong or is the eyedropper broken inside the three-way color corrector effect?

I'm on a Mac (Mojave - 10.14.6) and Premiere Elements 2019

I have footage shot on two different Nikon cameras and having a bit of a challenge to match the colors on both of them; the exposure parameters were matched on both while shooting, but upon reviewing them in post, I can see the colors being off 😕😕

couldn't fix it with the basic tools in 'fix' tab, so turned to effects; the three-way color corrector looks promising; I do have a bit of white space in the frame (i.e. parts of the frame that should be white) that shows as part of midtones in the tool (that's fine - it's part of the background and/so shouldn't be the brightest part of the frame); 

so I thought if I match that white part to actually be white on both pieces of footage, then the rest should be fine/better/improved too;

and I thought a good shortcut should be to use the eyedropper to indicate which part of the image I want to be white; well - when I click the eyedropper icon it all turns blue (as if active?) but as soon as I move the coursor outside of that small selection box, the coursor changes back to an arrow and the selection box turns back to gray; I can't point to anything, much less solve any of my issues 😕😕

the user manual just says "Use the different Eyedropper tools to sample a target color in the image..."

so as per above: am I doing it wrong or is the program misbehaving for me?