Your camera’s light meter is a reflected light meter.
Here’s how it works. And you need to simply accept and remember the following:
The in-camera light meter is designed to give a good reading when aimed at a mid-gray (“18% grey”) subject.
By implication, this means that when you aim at a non-midtone subject (like a dark subject or a light subject) the image will be incorrectly exposed.
In other words, because the camera “thinks” that it is looking at mid-grey it will try to render the subject as mid-grey.
One solution is to set your exposure manually while looking at a grey card; then using that exposure for your subsequent pictures taken in that light. That way I get pictures that are right regardless of the subject’s brightness.
Like these two taken at yesterday’s Sheridan College class, of two of my students:
 Darker subject, coat, camera:
 NBow a lighter subject, dress, wall:
Both were correct at the metered settings of 1/125th second, f/2.8, at 800 ISO. Which I measured off a gray card!
I have a question. If they are corrected using the grey card shouldn’t the color of the background (wall) be the same for both pictures?
The BRIGHTNESS should be the same, if the light on both walls is the same. Which is debatable. But the COLOUR Depends on your White Balance setting. I was probably on auto white balance.