Most side panel advertisements/promotions that I recall have a non-white background. However, http://i.stack.imgur.com/Ihs34.png (Programmer blog promotion) has a white background. When compared against the background on Programmers.SE (#f7f7f7), this shows a subtle but noticeable difference (a part of the screen looks oddly cleaner than the rest).
- Make it transparent
- Make it the same color
- Use a substantially different color (example: the Parents.SE promotion)
- Use a border around the image to set it off (example http://i.stack.imgur.com/yYx5g.png )
Not related to the color, but if someone is going to change it...
- The left hand side of the image image appears to be filled wrong (a bracket like thing?)
- The bottom right of the 'table' has two lines of pixels that are anomalous from the banner
- The font is lighter than 1px in places (might be rectified with bolding it)
- The bottom red 'steam' is cropped sharply while the top one has a 'blunt' endpoint.