Roses are made of a variety of colors and blue ones can occur naturally or with genetic engineering.
A natural way for roses to be bluish is through hybridization with other species. A common example is the crossing of Rosa Sauvageon, which has white flowers, and Rosa Foetida, which has pink flowers. The offspring from this cross have lavender-colored blooms but could eventually produce a bluish color variant if someone continually recrossed them with one or both parental plants resulting in increased amounts of energy being transferred between the two plants.