Red roses are the traditional symbol for love and romance, and a time-honoured way to say "I love you."
White roses represent innocence and purity and are traditionally associated with marriages and new beginnings. The white rose is also a symbol of honour and reverence.
The two together (although some older people might mention blood and bandages - ignore that its old-fashioned) means that after midnight last night, all Shell petrol stations were flogging them off really cheap because they were wilting. :o)