True blue remains a rare flower color in the plant world. Finding plant species that change their flowers from blue or blue-violet to white is even more fleeting. Often intense sunlight or age of the flower causes the blue pigments to diminish resulting in the fading effect. Many annual flowers that produce lots of seeds or are constantly being bred tend to cause mutations, leading to a single variety of an otherwise all-blue flowering plant to demonstrate the blue-to-white phenomenon.
If you're fortunate to live in the frost-free tropical regions, three species of Brunfelsia display blue-violet flowers that fade over the course of three to four days. Commonly called yesterday-today-and-tomorrow, late winter and early spring flowering species include Brunfelsia grandiflora and Brunfelsia pauciflora. On the first day of flowering, a blossom bears a rich blue-violet color, and then fades to pale blue-lavender or sky blue on the second day, and then white by the third day of exposure. Another species, Brunfelsia australis, blooms in early to mid-spring with a delicious, more intense floral fragrance. It is also known as Paraguayan jessamine. Consider growing these tropical shrubs as houseplants in a warm solarium or sunny bay window.
Brazilian Potato Tree
Also a subtropical tree that should not be exposed to subfreezing temperatures, Brazilian potato tree (Solanum wrightii) bears five-lobed flowers year-round when temperatures and warm and sunshine plentiful. The flower first opens a deep violet to indigo and the next day fades to light blue and is white by the end of its life. Heat and light intensity affects the floral color display.
Those gardeners not living a tropical climate can enjoy dark blue petunias as summer annuals. Normally a deep, perfectly blue-colored petunia that fails to retain that flower color intensity might be seen as undesirable. One exception of note is a member of the Shock Wave series of petunia and is named Denim Blue. The trumpet-like flower opens a deep blue and gradually fade to light blue or silvery white, creating a plant decorated with various flowers with different blue tints. Azure Blue petunia in the Pearls series also fades, first from deep blue-purple and then to white.
Looking into new plant introductions developed from naturally blue-flowering plants may yield a new variety that fades its flowers from blue to white. For example, search catalogs for love-in-a-mist (Nigella damascena) and locate blooms that fade from deep blue to sky blue, such as selection Dwarf Moody Blue. Cup flowers (Nierembergia scoparia) open pale blue but their petal edges fade white over time, creating a blue-to-white effect when planted en masse.