What causes the outer row of leaves to lighten in color?
What causes the outer row/rows of leaves to get light in color? This doesn't happen on all species. My best light source is a large east window. I am fertilizing with Miracle Grow African Violet liquid plant food every three weeks. I use rainwater and water from the bottom.
The condition your African Violet leaves are experiencing is known as "bleaching".
It can be rectified by one of two ways:
1) increasing the amount of nitrogen in your fertilizer
2) reduction of light intensity or, if growing under fluorescent lighting, the length of day
Violets favor 12 hours of fairly bright light in an east window like yours or a south window with some filtering.
African Violets can be sensitive to many things, sunlight, watering, humidity, and fertilizing.
I believe the lighter leaf color you are describing could indicate they are needing more fertilizer.
Please read the attached article which give you very good instructions for a fertilizing schedule.