1. As a symbol, a rainbow can have several meanings. It represents transfiguration, different states of consciousness; the meeting of heaven and earth; the bridge between this world and paradise; access to the other worlds; the union of heaven and earth.
A rainbow also stands for completion.
Sometimes it is used as a symbol for restoration of order.

2. The Rainbow project is the name of one of the Philadelphia / Phoenix Time Travel Projects. See Phoenix Project I for more information.