Hi Dan,
Thanks for trying out Google Web Designer.
For color keyframe animation, you might want to try using a div tag tool instead of using shape tool (rectangle, oval and line).
You can draw a rectangle with the tag tool, insert keyframes and change the color at each keyframe. That should create color animation.
GWD does not support color animation for canvas shapes, but you can change the size of the shape elements in Timeline.
I hope this helps,
Thanks,
Mariko (GWD team)