Getting the color from a beamer theme?

A beamer presentation uses several colors. beamer provides commands for using colors of the presentation elements. Choose the element of which you would like to use the color and apply it, for example:

{\usebeamercolor[fg]{structure} text}

prints text in a blue color, with Singapore theme.

Here fg means foreground, bg means background, instead of structure you may use title in head, section in head, normal text and many more. Have a look into the beamer manual for learning more about using colors.

All the informations on color themes are in the directory Beamer\Base\Themes. But it's easier to write color=block body.bg to use the background color of the body of block, independently of the theme chosen.