To see a rainbow in a dream, is prognostic of unusual happenings.
Rainbows are colorful bridges that fall across the sky, but we can not walk across them (or use them to get to our pot of gold).
Usually a rainbow follows a rainstorm.
If so, you have weathered a difficult time that is coming to closure, this dream symbol may represent your optimism.
Generally, rainbows make people smile and feel happy.
Thus, some may consider this dream a sign of your good luck.