Applying point color selection to mask

I want to change the color of part of a photo to match the color of a different part of the photo. I have created a mask of the area of the photo I want to change the color of, and selected the color I want to change it to with the point color dropper. How do I apply the selected color to the mask?

By @rdgipson

This is a little more complicated in Lightroom Classic because it lacks the on-image color samplers that you can leave in place for precise color readout. These are found in Camera Raw and Photoshop, but mysteriously missing in Lightroom Classic. And Lightroom/Camera Raw masks are not as graphic-design oriented as Photoshop layers, so you can’t take advantage of easy color-changing features such as blending modes. 

But you can still get it done. The demo below shows a blue door that’s been masked. The first thing the demo says is that you should be careful with the terminology. What you are describing doesn’t sound like the feature specifically labeled Point Color. It sounds like you want to apply an absolute color value, not make a relative visual color shift. Which means this is not about Point Color after all, so the demo starts out by saying “Don’t need Point Color.” (Point Color is for subtle color tuning, not fundamental color changes.) The Point Color sampler is not like the Point Sample setting for the Eyedropper tool in Photoshop even though they sound similar, because the Point Color sampler is only a starting point for applying Point Color and (unlike Photoshop) not for all other color adjustment features. 

What the demo does instead is change the mask value for Hue. This is often a more direct way to change the basic color of an object. Of course you can also change the mask values for Saturation and Exposure/Whites/Blacks to get the color just right. You can actually use any masked color adjustment you want such as Curves or Temp/Tint, it’s just that Hue can be a more direct first step when you want to make a fundamental color change.

As you do this, to verify what color value is under the pointer, we refer to the RGB values under histogram, which I highlight in green at the end.

(The colors might look rough in the demo because the Adobe forum software degrades the color of GIF animations. The color looks fine in the file I uploaded.)

Let me make sure I understand you ... you want to point at a color with the Point Color dropper, and then ... well this is the part I don't understand ... what does it mean to apply that color to a mask?