There are a few reasons why roses show discolouration that are entirely natural and don't indicate the flowers being in poor condition.
Guard Petals (all roses)
the outer petals on a rose are called guard petals. These have been protecting the rose in bud and are exposed to the elements. They are by their very nature discoloured and usually dryer than the other petals. We leave them on to protect the rose in transit. Although they will become less visible as the rose blooms, they can be removed safely. Instructions of how to do this can be found in the care guide sent with the flowers.
Green-tinged outer petals (pink and white roses)
white and, to a lesser degree, pink roses sometimes arrive with green-tinged outer petals. These petals have retained more chlorophyll. Chlorophyll is the natural pigment plants use for growth and strength, and in white roses it can sometimes remain visible at the outer edge of the bloom. Natural variation between varieties means some white roses show this more than others. They are a natural feature of fresh high-quality flowers, not a fault.
Blackened petal edges
red roses naturally have very high pigment levels, which makes their petals more sensitive that lighter coloured varieties.
Because of this, the outer petals can sometimes develop darkened or almost black-looking edges.
This is most commonly caused by natural handling and environmental factors, rather than damage or age.