Allow color prop to be empty?
Hi, color prop has
```
ColorPicker.defaultProps = {
    color: {
      h: 250,
      s: 0.50,
      l: 0.20,
      a: 1,
    },
  }
```
it it possible to allow this prop to be empty?
Like allowEmpty option in this https://bgrins.github.io/spectrum/
Thanks!
