(this node was empty, so i'm filling it)(that's early noderese for nodeshell rescue, btw)
In the language of flowers, a red rose is for passion(ate love). Other roses were for other kinds of love, but red - for intensity and blood, you know, the associations we all overused in high school poetry - red was for passion. Deep red, some sources say, is for unconcious beauty. Not the rohypnol kind, but the kind that causes bloodrushing first crushes and longing lurve. The kind that aches behind the eyes and all kinds of other untoward places.
A red rose was the symbol of the House of Lancastrians in the War of the Roses. White was the symbol of the House of York. When peace was attained (through marriage), the Tudor rose was invented, a red and white rose symbolizing unity. In combination, red roses and white roses symbolize unity too - though many sources say this, not too many of them trace it to the Tudors.