text: Roses are especially difficult to obtain blue/violet flower colour. Lack of F35H and unfavourable vacuole pH were the main obstacles. A lot of cultivars were screened to choose the proper one for genetic modification. Finally, flowers with violet/blue hues were obtained by overexpression of viola F35H, down regulation of endogenous DFR and in the same time overexpression of iris (Iris x hollandica) DFR. In the result of those modifications flowers accumulate almost exclusively delphinidin type pigments in the petals.
  Additionally, hybridizers throughout the history of rose cultivation have made several strides toward producing rose varieties with colors in the lavender, violet, and mauve color families.
  These colors were the height of fashion especially in the late 1800s, when the industrial revolution made synthetic color pigments inexpensive and widely available for the first time. Bright shades of royal purple, mauve, and blue naturally became extremely popular and fashionable because these colors previously were only available to extremely wealthy people. The pigments to create these colors were previously very scarce.
  Several classes of garden rose were created with magenta and violet flowers during this time period to reflect the growing trend in popularity of these previously luxurious and rare colors.
  Notable examples of popular historical roses which are still grown today by rosarians include the gallica rose Cardinal de Richelui ; the hybrid perpetual Reine des violettes, and the setigera rambler rose Veilchenblau.
  Their violet flower colors are due to complexes of cyanidin with sugar molecules, metal complexes, and tannins naturally present in the flower petals.
  In the early 1900s, a new species of rose called Rosa foetida bicolor was introduced into world commerce from the middle east. It has flowers which are bright shades of butter yellow, orange, and velvety blood red, which introduced new genetic traits that serendipitously and coincidentally created a pathway toward new lavender and blue pigments that are independent of delphinidin, a blue pigment not naturally found in roses.
  That pathway involves the final stages of flavanoid pigment synthesis which would normally cause flowers to appear yellow or orange. This new species carried small traces of unused genes that allowed production of another type of blue pigment called rosacyanin, which most roses evolved to stop utilizing in favor of producing flower fragrances to attract pollinators.
  Rosacyanin allows roses to come in delicate mauve, lavender, and true blue shades.
  These colors can be seen in the hybrid tea roses Sterling Silver, Blue Girl, and Blue Moon, among others, which descend from yellow roses. Most notably a popular yellow hybrid tea rose called Peace, which was named to commemorate the end of World War II, was used extensively in hybridizing, and fathered most of the original lavender hybrid teas.
  In 2004, Japanese company Suntory produced a blue rose, named Applause.
  Further hybridizing advancements, scientific study, and possibly further genetic engineering will be necessary to concentrate these natural genetic  factors and cofactors before roses will be able to come in deep shades of true  blue.