Apparently I have to explain how digital images work.
Every single digital image is comprised of three channels. Red. Blue. Green.
Here is a picture of Daisy, chosen for it's bright blues and red-oranges.
Now let's looks at what this image looks like behind the scenes. The magic 1s and 0s that make this image what it is.
Here is the red channel:
The green channel:
And the blue channel:
Every single possible color in that original image is a result of mixing these three colors.
When you overlay these three images on top of each other
You get the original image. Magic.
So let's talk about lossy compression.
Each pixel has an exact percentage of red, blue and green. That data is affected by the lossy compression, and as a result, the balance between the channels changes.
Areas that previously had no green pixels at all, suddenly get them, because the data in the channels gets mixed. I've highlighted just some of the new green pixels here, but you can also see new RED and BLUE pixels in areas they shouldn't be, too.
This is completely normal, completely expected behavior.