Illness in the family is keeping me busy, so this will be quick.
I saw this photo in the Economist magazine.
It reminded me that I should throw out some examples that use dark and light to define an object. You might think that a blue industrial building against a blue sky would yield a building that "melts" into the background. It can, but does not have to. The sky has an amazing amount of variation, even if it is cloudless. Try taking a series of photographs of a clear blue sky, pointing in all directions including straight up. When you compare the photos side by side, you will notice a lighter horizon area, and also a lightening toward the area near the sun. This is not new or earthshaking, but is good to know if you are illustrating architecture.
So, if you are interested in making a building stand out you can simply reverse the grading of light to dark so as to make it contrast with the background. Again, simple and obvious, but all too often overlooked.
Sketching and Rendering in Pencil) shows that anything can be used for the defining contrast. In this case the sunlit wall at the right is nicely shown off by the dark trees behind. while the dark roof works against the lighter sky.
In portraiture the same rule is often applied. A figure in side or three-quarter lighting will have a dark and a light side. Playing this off of a graded mid-tone background can pop the subject out nicely.
A reflective glass building can have a lot of complex patterns happening, but it still needs to stand out in some way. I decided to try a dusk view for this tower in China, creating a glowing facade at the base, and a dark on light contrast at the top.
This pencil drawing of a highrise proposal at Canary Wharf in London uses a reverse value trick that goes back 100 years and more. Just because it is old doesn't mean that it isn't effective.
In architectural illustration reverse values work best with long structures like towers. It can also be used with long, low facades. In the Rainbow Bridge US Customs Inspection Building at Niagara Falls, the sunlit end on the left is placed against a dark rack of clouds, while the other end is dark on light. This helps to break up the necessarily long building, giving the image more interest. The rainbow was my own "over the top" idea which was not in any way the responsibility of the architect or client.
There are no limits to the variations you can try once you start playing one plane off another. And the strong value structure leaves you open to color experiments.
Of course you don't have to paint gradients across the entire image. You can darken or lighten at the edges where it counts, and let the viewer's imagination do the rest. The slight shading above the reclining nude defines the shape crisply, while the parallel dark and light lines anchor the figure to the ground.
This barely touches on the subject, so I imagine I'll be back sometime.