fill: color, separate from stroke?

@desandro possibly obvious request, but I wasn't able to find in issues/docs. We have shapes like that we'd like to animate.

My expectation would be as in SVG to have stroke and fill to define color. It doesn't seem to be the case here - fill in zdog is just a flag. I would like to avoid creating two shapes just to make stroke color different from fill. Do you think it'd worth extending fill to support strings? Or you know some alternative? One hack would be rendering into SVG and styling shapes via CSS.