I normally change the Backcolor property. if you want to know what to change it to you can open a forms properties and go to the Backcolor property - then click the ... build button. This will open the color dialog window, here you can choose a color of the standard template or you can define a custom colour by either draggin the cross around or by inserting the RGB values. Once you click OK you'll notice that the background property's value has changed acoordingly.
ie. to change the background color of a form during run time you can put a code like this:
Private Sub cmdChangeColor_Click()
Me.TestID.BackColor = 65280 'changes textbox named TestId's backcolor to bright green