Payne's grey is a color that artists use. It's not just one color like red or green, but actually a mix of a few different colors like black and blue. It's a really useful color because it can be used to make things look darker, like shadows or clouds.
Imagine you're drawing a picture of a big fluffy cloud. If you just used white to color it in, it might look too bright and not like a real cloud. But if you add just a little bit of Payne's grey, it will make it look more like a real cloud with shadows and depth.
It's sort of like when you mix colors in paint or crayons. If you mix red and yellow, you get orange. It's the same idea with Payne's grey, it's just a mix of different colors to make something new.
So, Payne's grey is a color that artists like to use to make things in their drawings or paintings look more realistic and have more depth!