Why doesn't vterm take the load-theme theme

If I set load-theme wheatgrass (a nice dark grey with lots of soft greens) in config.el and then run vterm, it is still the eye burning white background with blue and green text. (looks like default xterm). Is there a way to get vterm to have the same color scheme as the rest of emacs or do I have to edit the xresources every time I want to change the vterm theme?