How do I display color value slide bar (not sure what it's called)?

Hello, I'm taking a class in basic value studies for Photoshop. I'm new to the software. Not sure how to display the gray scale to change the gray value for a brush? It's the sliding bar you see above the color bar in the picture below. Can't seem to find it when I open up Photoshop. Apologies if I got any terminology wrong.