Set color to empty

Hey there,
it's not possible to reset color of the iris color picker to an empty value:
`jQuery( element ).wpColorPicker( 'color', '' );` is not working here.
I solved it in following way:
`jQuery( this ).find( '.wp-color-result' ).css( 'background-color', '' );`

On initialization it works fine.

PS: I know it's the wp-color-picker, in iris it would be something like that:
`jQuery( element ).iris( 'color', '' );`
`jQuery( this ).find( '.iris-result' ).css( 'background-color', '' );`

Start by reproducing the empty-value call through jQuery(element).wpColorPicker('color', '') and compare it with initialization and the equivalent iris('color', '') behavior. Check the .wp-color-result and .iris-result entry points; done means resetting the picker through its API clears the displayed color without requiring direct CSS changes.

Written by the indexing model from the issue text.