Everyone has his own eye for beauty so we may not all agree that this one is beautiful. On the "pretty scale", though, it rates pretty high. The reason is the use of color. Although there are many colors in this painting, it's background is the scale of windsor yellow to sap green. The greenery in landscapes is primarily sap, but certainly not only sap. Nature's green is never just green but includes an array of blues and purples in the shadows and yellows in the light.
The complement of green is red so the flower's red values say "pretty" when used with this green. I would have loved a brighter cad red pop in the flower but I didn't want to chance moving the focus from butterfly to flower. It is a painting about a butterfly visiting his choice of many lovely flowers. He is in love with this one. It is not about a vivid, eye-popping flower attracting some random butterfly.
The lost and found edges (blurry and sharp) also lead us to the butterfly and his delight.
My delight? That someone in California loves this one, as much as I do. The photo does not do it justice. Tomorrow it goes in the mail, sealed with a kiss, to it's new home.