Thanks for the feedback. Although the different colors is a great idea I think we are liking the aesthetic of the dominoes right now, and also have other domino types planned out such as wooden. I also found another popular domino game that used colors just as you suggested so would like to differentiate as much as possible.
For now I added little "here" blurbs that the dominoes say when Double Blank pulls out a matching domino. It isn't perfect, as sometimes you are juggling two dominoes at once, but I think it helps a bit. What do you think?