To clarify it can be a colour, a technique, a theme. Here are some ideas to get you going.... Christmas, cat, Cucumber Crush, chalk board technique.
For my card I have used Christmas and a cat :)
Stamps: Simon Says Stamp 'Furry Christmas' and sentiment from My Favorite Things
Ink: Memento Black Ink
Other: Copic Markers, white texture paste, star stencil from My Favorite Things