Woah, take's me back to late 80s computing when colors were few but paint programs all used to have patterns in them.

There's a really nice additive effect with patterns that can give a designer a way to show combinations of things together in a way that color really can't (bonus it's better for some visual impairments). For example, take a series of lines for one value:

   \ \ \
    \ \ \
     \ \ \

and a series for another kind of value

     / / /
    / / /
   / / /

put them in the same visual space and simple add them together

   x x x
   x x x
   x x x

You can also add in vertical, horizontal lines and even line width (and even line color over a baseline color) and you can encode a ton of different values into a single graphical area.