Animation clip and color curves

Has anyone else tried to animate shader colors using the an Animation clip? Either we're doing something wrong, or it's legacy/deprecated, or the shader is wrong.

In the clip I'm changing position, so I know it's being run. And the shader is a custom material using Diffuse, so it has a Main Color attribute, which is defined as _Color in the shader, which seems to tie up with the Animation component's "Animate colour" option.

Are there any caveats that we're missing?