The term Rainbow Bridge is used in several very different ways - which do you mean? One of the most famous is the bridge connecting the USA and Canada at Niagara Falls; and that gets its name because Niagara like other waterfalls creates the illusion of rainbows when you look at it on a sunny day.There's an excellent photo of the bridge with a rainbow in front of it on a Dutch website - http://www.cuci.nl/~quadpuss/Niagara%20Falls.htm