How to lessen armpit discolouration?

I don't even know if thats what it's called, but I'm poc and I hate that my armpits are a different color to the rest of my skin. I shave and exfoliate but it doesn't help. It makes me insecure and feel like I always need to wear jackets so people don't notice, although realistically I know no one will care that much.

Is there any way to stop or lessen that?