Change default color

[ItsPierre]

We should change the default color from white to black or primary since it is confusing, if the component is used and you don't see anything.

An alternative would be to remove the default color and make the color required.

[johannes-huther]

I'd argue that primary or success would be gould candidates, but they only work together with vuetify. Maybe we could check if they are defined before?