When creating a sprite or label you generally do not need to worry about UIWidgets, since every sprite, label, etc already have a UIWidget component included.
For the cell: I would create a new UIWidget and use it as a base for the cell and then add a UISprite and UILabel as children. If you do not have any performance issues having a simple sprite with one color as a background should be fine. If you make the sprite texture white, you can color it using the sprite settings and do not need differently colored sprites.
I would probably have a setup like this:
+ GameObject with UIGrid component
-+UIWidget(your cell object)
--+UISprite (background color)
--+UILabel