When should I use an em-dash?
Rather than using two hyphens, consider using a single em-dash.
Em-dashes can take the place of commas, colons, or parentheses in your sentences. Most word processing programs autocorrect two hyphens in a row into an em-dash.
Note the emphasis in the following examples:
A multitude of hues (red, orange, yellow, and brown) washed the trees in color.
A multitude of hues—red, orange, yellow, and brown—washed the trees in color.