Most artists agree that, in painting the figure, tan lines are best avoided: The whole idea behind painting nudes is to explore the body’s elegant lines without the distracting clutter of the lines that clothing adds. Tan lines add those lines, even without the clothing.
But sometimes they are, in themselves, an interesting subject. Here’s my model Mystery, clearly and gorgeously illustrating the fact.
By the way…this picture (check the enlargements) displays an impasto effect, which in oil painting means the thick application of paint. But the effect is an illusion: This is a computer graphic, as flat as your monitor.