Thanks Xed. Great feedback as usual. Coloured pips is a good idea and I love the `?` idea.
I will have a think about forcing starting doubles. I've considered it but I'm resisting rigging the deal because it means having one more thing at the start of the game that is difficult for the player to absorb. In my many, many hours of play testing, I think there was one time I got an opening hand that couldn't be played strategically to make it to the second hand, with or without doubles. Maybe having 1/100 like that is too much though, and I will think about visibly shuffling dominoes back into the pack until the first double is pulled out.