Speed of Dark???

Hi All

In the questions and answers page of Tuesday's Daily Mail is the following
question.

Q: Images of distant galaxies contain both light and dark matter that is
only visible to us after millions of years of travelling across space. Does
this mean that dark, like light, has momentum, and if so what is the speed
of dark?

Isn't darkness simply an absence of light? Should be interesting to see what
answers they get ;-)

Neil