Why do some Roses have black edges?

1.  Why do some Roses have black edges?
Black edging happens for two reasons: light and temperature

Explanation:
UV light–
Roses are grown in areas with lots of intense light energy. Production areas close to the equator (Colombia and Ecuador) get 12 hours light      everyday of the year and the light energy (luminosity) is strongest at the equator vs. northern latitudes.

Pigments in red roses are particularly sensitive to “sun-burning”. This condition is genetic to red, brown and purple rose varieties

UPSIDE: It is this strong equatorial light that also provides us intense colors

Temperature:
Greenhouses in Latin America are mostly not heated so when there is a big difference between daytime and night time temperatures, roses respond in a way that the pigments concentrate.  In yellow and pink varieties, concentrated pigments appear as red flames or    intense color chips, but in red varieties, pigments appear black.

UPSIDE: The wide variance in daytime—night-time temps gives us HUGE head sizes

2.  DO BLACK EDGES AFFECT VASE LIFE?
No, not at all. The down side is simply the effect on aesthetic appearance

3.  WHY DON’T GROWERS PEEL PETALS SHOWING EDGING?
•   Peeling opens the bud structure and blooms pop fast
•   Peeling triggers the internal production of ethylene which shortens vase life
•   Ethylene gas is produced as a wound response
•   Peeling distorts the bud shape. No one wants a Hershey’s kiss shape rose
•   Peeling the guard petals leaves roses susceptible to mechanical damage inherent in  transit and handling
•   When roses open, the dark edges re-curve down and are not visible

4.  WHY DO WE GROW VARIETIES THAT SUFFER EDGING PROBLEMS?
These varieties are selected because they perform well in the growing conditions of Latin America (e.g. large heads, strong, long, straight stems, good opening)