Complex sentence: For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, but in the same scene viewed at dusk, the contrast is reversed, with the petals appearing a dull red against paler green leaves.
Split into simpler sentences: For instance, notice the bright red of geranium flowers against the dull green of their leaves in bright sunlight, and then view the same scene at dusk. The contrast will be reversed, with the petals appearing a dull red against paler green leaves.