you are correct that tool cards have a purple outline and actions have a blue outline. I think having a colorblind option with the full word or first letter on the card makes sense. Though if you didnt memorize what the card did you probably shouldn't be playing the card without double checking what it does. Tools all need to be used directly on a resource and actions are all used without targeting anything for example even though aquifer upgrades your resources because you dont target anything its a action.