The color of the rose has its own symbolism: white stands for purity, red connotes passion, yellow indicates platonic friendship and pink stands for grace or gratitude. Legend says Cleopatra lured Antony into a room filled with rose petals knee-deep. As for the Greek symbolism, here's a description of the rose's origin taken from http://www.rosemagazine.com/
"Flora, the deity of flowers, was walking through the forest and found the body of a beautiful nymph. Sorrowful at the sight of the lovely creature dead, she decided to give her new life by turning her into a flower whose beauty surpassed all others. She called on Aphrodite to give beauty, brilliance, joy and charm; Zephyrus, the west wind, to blow away the clouds so that Apollo, the Sun, could cast warm rays upon it, and Dionysius, the god of wine to give nectar and fragrance. When the new flower was complete, Chloris placed a crown of dewdrops over her and named her the Rose, Queen of Flowers. Aphrodite presented the Rose to her son Eros, the deity of Love. The white rose became the symbol of charm and innocence and the red rose the symbol of love and desire."