There are hundreds of species of aphids, I’ve seen green, white, black and yellow.
I’ve only found them on my tea roses and crepe myrtles but they’ll attack almost any plant.
Aphids reproduce sexually but can reproduce asexually and new aphids take only 4-10 days to reach maturity. The average aphid has a life span of about a month.
Aphids damage plants by removing the sap, some will also feed on foliage. Most also secrete a sweet sticky substance which attracts ants who will feed on the sap. The sap also attracts a black sooty mold fungus (Capnodium spp) which will cover the leaves of a plant.
I prefer to treat aphid infected plants with orange oil which you can find in most nurseries. Mercer Botanical recommends blasting them off with a garden hose in mid afternoon, the afternoon sun bakes them.
Natural predators of aphids include lady beetles (convergent, pink spotted, and scymnus species), green lacewing larvae, and syrphid fly larvae.
Other than seeing the aphids and black soot on the plants you might also see malformed flower blooms or leaves, or wilting of young stems on the plant.