Beamer has a few built in colour schemes which it is relatively easy to switch between.
In the preamble add the line
where xxx is one of the following
Alternatively you can define your own colour scheme using the following code before the above line
where 0.125 is the intensity of red, 0.5 is the intensity of green and 0.25 is the intensity of blue. Then replace xxx with colourname in the \usecolortheme command