Here is a good way to experiment around with backgrounds when you are unsure of what you want. Using your digital camera, take a picture of your painting. Print two or three copies of the painting on glossy photopaper. Now, you can paint on the photo with your oils. Do several different background plans. Choose the one you like best and use it as a reference in doing your painting. Saves time and a lot of overworking and wipeouts.

Students often ask me, "What color should I use for the background?"
Background colors can be analogous to the subject in which case there is usually good harmony resulting in a somewhat monotone painting. Neutral colors are also good choices as they will recede bringing the subject closer. Opposite colors are the third choice. Opposite usually refers to temperature (cool vs warm). Careful consideration must be given to dominance. In other words, from a compositional standpoint one would not want equally dominant warm and cool colors. Variety is more interesting.

Yesterday my student, Janie, and I had a discussion on backgrounds. Janie likes to do her backgrounds first before getting too envolved with her main subject matter. I usually go straight to my chosen center of attention and develop it rather completely first adding just notes of backgound while I work. I find when I do that my back grounds remain secondary in importance and are more supportive to the composition. Backgrounds are akin to choosing a good frame. I believe you frame a picture rather than picture a frame. So many otherwise good paintings are greatly diminished by poor framing. Likewise, lack of attention the the background can be the demise of a painting.