Is an ant red

They are not necessarily black or red; some are both and some are neither; many are brown, some of them very light brown and some quite dark brown. Some, especially those living in the dark, are a pale yellow colour.

As for why they are commonly black or red, the black colour may be useful for absorbing warmth or protecting the animal from ultraviolet. However, especially large species, conspicuously coloured in red or black or both, and with typical conspicuous ant-like behaviour, would be likely to scare off creatures that might otherwise attack them. It would be a warning that these creatures are ants, likely to bite or sting or have a sharp smell, and to attack in their thousands, so that they would be best left alone.