I'm unfamiliar with the tutorial, but you should definitely be able to animate the grass in the vertex shader according to vertex colour, if that's what you're after.
Although, all of the grass vertex animations I've seen use the UVs to control which parts of the grass are affected, and you could probably use your vertex colours to control the direction or something. Could be pretty cool.
If you haven't written such a shader before, I think that a similar shader is included in the built-in shader source
(although those might be using Shaderlab, rather than the more standard -- and more understandable in my opinion -- standard vertex and fragment shaders).
If you get really stuck I can look at whipping one up when I've got some time.