If you are trying to classify a specific termite colony into a group, you need to look at the soldiers and the alates, the winged, unmated reproductive caste, because worker termites across groups tend to look the same. Also important is the appearance of the damage wood they consume.

Identification factors for subterranean termites are:

Alates (swarmers): Dark-brown to black in color, about ¼ to ½ inch long with two pairs of wings that are very close to being equal in length.
Workers: No wings, about ¼ inch or less in length and cream colored.
Soldiers: No wings, large mandibles (jaws), termite colony defenders, are creamy-white in color, but their head is often brownish in color.
Appearance of damaged wood: Since subterranean termites build their nests underground, damaged wood usually has an accumulation of soil or mud within the tunnels of the wood they are eating. Since subterranean termites only eat the softwood, damaged wood appears to be layered, the result of the workers not eating the hardwood portion. In addition, subterranean termites feed “with the grain” rather than across the grain, as do drywood termites.
Location of the nest: As their group name suggests, the nest is usually found below ground. Nests may be found above ground, but only when sufficient moisture conditions are available to support the above-ground nest and the colony is old and well established.