I'm guessing you used code similar to the following to set the foreground color item's color:
btnTextColor.ForeColor = Color.Green
To set the background button's image, use code similar to the following:
btnBackgroundColor.Image = My.Resources.Green
The My namespace is covered briefly in Lesson 36 so you're getting a bit ahead but in a nutshell My contains shortcuts to useful items including project resources. In this case, the project includes files named Blue.bmp, Green.bmp, etc. so by default it gets resources holding the corresponding images named Blue, Green, etc.
The line of code above sets the button's Image property to the Green resource so you see the corresponding bitmap.
I know it is redundant, but I just wanted to do it (I was playing and having fun).
That's an excellent way to learn this stuff! Think of changes you'd like to make and then try to make them.
Let me know if you have other questions or have trouble getting the images to work.
(Also post a review when you have a chance!)