Great article and good CSS transition. Though I’m suprised the other css-ways are not mentioned:

• The first one is to change the background-color, and using a rgba-color with opacity. This is great for colors that are close to each other.
• The second one moves the entire gradient-layer. This is only usable in fast animations that are allowed to have a directional feeling in it.

I made a codepen out of it: 
http://codepen.io/anon/pen/MywKwQ