It's not you--there's apparently a bug or at least a limitation in Hub Link/Link to Hub's implementation of some color commands. I described this issue for another poster in this thread a while back, but it appears to be the same issue you ran into:
As I mentioned there, there are two solutions: use Hub Connect (a community-created, more powerful alternative to Hub Link/Link to Hub), or also add the Hue Bridge integration to the other hub (there are pros and cons to this approach, two cons being that it's more work for your Hue Bridge getting polled from both hubs and the fact that devices may briefly be out of sync on both until the poll updates them)--but it's definitely a possibility.
