There are multiple metric units to choose from! This tutorial goes through the process of choosing the best metric unit to use for measuring the mass of a given object.
The most common aphids on houseplants are the light green ones (pear aphids), but aphids can also be found colored pink, white, grey and black. Additionally, winged aphids can appear when colonies are established and fly to infect new plants. Juvenile aphids (nymphs) look like smaller versions of the adults.
Producing wings is a protein-intensive task, so aphids wisely conserve their resources and their energy and remain wingless. The aphids do quite well in their apterous state until food resources run low, or the host plant gets so crowded with aphids that the group must disperse.