Bob Green calls variegated African violets "peacocks of the violet world" because of their "plumage" or leaves they possess, making them stand out from others with green foliage.
Variegated foliage was discovered by Mrs. Tommie Louise Oden when she ordered leaves of White Pride from Clyde Rollof. It was a white double plant, but when she planted the leaves, she discovered different colored leaves. She grew them through nine generations, and they came "true". Up until that time variegated plants were unstable.
TYPES OF VARIEGATION:
Crown: The center leaves are often totally variegated, then as the leaves mature and grow out and away from the crown, they gradually gain green coloration in a sprinkling effect. The heart of the leaf remains initially variegated, and the green gradually radiates into this variegation until, as a large mature leaf, only a stippling edge of variegation remains, along, with a small heart sometimes.
Mosaic: The variegation appears as uniform stippling or marbling covering the entire leaf surface, and the leaf is never without variegation even though it may be faint at times. There are very few of this type since it were introduced many years ago. They are very stable and not affected by temperature change or high nitrogen fertilizer. This "mosaic pattern covers the whole leaf and is a serious defection or mutation and very few of them reach maturity. These plantlets are puny or hard to grow. There are very few good show plants, both Emperor and Lillian Jarrett have proved to be real winners.
Other Variegation: The AVSA registration form for new hybrids lists the following items to check under leaf description: "If variegated-type of variegation ___Crown___Mosaic___Other. The "other" apparently includes all forms of the Tommy Lou. There is also a line to denote the color of the variegation. I think many hybridizers now would tend just to call a plant variegated unless it was a crown or mosaic.
Tommie Loue type variegation is more stable under a wider range of conditions than crown variegation. Those varieties with crown variegation can loose almost all variegation in the summer heat. However, the new leaves will start variegating again when cool weather returns. Both crown variegtes and the Tommie Loue types will do better if you place them closer to the floor (for example, the lowest shelves of your light stands) where the temperture is cooler, since heat naturally rises. The mosaic variegates are not affected by temperture and heat, and their variegation will remain constant.