Hello Jef, there have been posts in the past about background images that are multidimensional, wildly patterned and colorful for WikiTreers who have visual issues. For the most part since this was written up about 3 years ago, I have noticed a reduction in the use of background images. There were recommendations for background patterns that weren't visually distracting and did heighten the information in the biography.
Personally, I hope to find 'something' relevant to the profile to add as a profile picture, a headstone, a photo, or some such thing to enhance the biography. On occasion, in addition to finding a photo, I come across a headstone for the person. Both are relevant to the profile. In this case, I will use the profile picture, then use the headstone for the background. There is a 'however' though. If the headstone or image is so large that one cannot even understand or appreciate it, I skip using that image for the background and just leave it blank. Some headstones, though, are small and clear enough that they actually do enhance the profile and fit well with the photo of the person...kind of a visual life to death photo story.