Improving Greedy Bankers for Colour Blind Players - Help Needed!

Hi everyone. One of the issues that came up at Eurogamer Expo that I really wanted to fix was the fact that the game was very difficult for colour blind players. This is something I really wanted to fix, because I don't want to lock anyone out of playing the game over something that's easy to fix.

For example, here's a screenshot from the four-colour version of the game...



... and the same screenshot as viewed by someone with red-green protanopia (as far as I know, the most common form of colour blindness). I used the Vischeck web tool to simulate the view (which seems to have stopped working today, unfortunately).



The problem is fairly obvious! The easiest, and hopefully most effective way to do this, was to add symbols to the gems to make them easier to distinguish. These can be toggled on and off by the player. My question is, for any colour blind gamers out there, does this make any difference? Is there anything I can do to improve the effect?

Here's the game board without symbols...



... and here it is with symbols...



Any pointers and words of advice?