Unfortunately we don't have support for this behavior yet. There is an open request for this feature which you can vote for here:
We would be grateful if you took the time to vote and add further comments there if you feel the need. This way, we will be able to better assess the need for the feature.
Has this feature been implemented or is there a workaround? Still trying to change the fill color of buttons created in photoshop.
It didn't work for me (even after viewing a few tutorials), but I did eventually find a site that converts png to svg for you so I've been using that and then importing which works just great!