This is the color tool. When you tap this tool, you will see a color wheel, a slider, and three tabs.
Move over the color wheel to see colors displayed in the outer ring. When you have selected your color, tap "Use".
The slider adjusts the color brightness. This is how you can get a black color.
After you tap "Use", the color will be added to the "Recents" tab.
At the top left of the color wheel is a favorites button. This will add whatever color you see in the outer ring, to the "Favorites" tab.
To delete either a "Recent" or a "Favorite" color, tap the "edit" button that now shows in the top left corner. You'll see a delete (x). Tap that. When you're done, tap "Done"
To use a color stored in the "Favorites" or "Recent" tab, select it, and tap "Use".