The black cards are "Idea" cards. There's about a 10% chance that while working alone, without tools, your settlers will think of combining cards together to create something new. For example, Worker & 2x Fiber creates string, while Worker & 4x Fiber creates rope. The game recognises that because you know of Fiber, you can use that to make something else. Think of it as free research.
I'll have a message appear explaining this, as well as change the plain black card to a lightbulb.
Another thing I will have to work on, based on your feedback, is the need to put across the idea that tools are the most versatile recipe in the game. You can craft them using any combination of Sticks, Stones, Bones or Flint. For example, 2x Sticks will produce a tool. Adding string to the recipe will allow you to produce more durable tools.
Again, I'll include a message highlighting this when the player uses their last tool.
Strangely, the game is already set up to balance out the resources you have. If it recognises that you have more water than stone, it will prioritise stone. Odd that it's taken 33 turns to get your first one.
Bugs
Might I ask what browser you're using to play the game? I notice that the Todo and Year texts are not in their correct places. This won't be a problem with the windows version, but it's odd it doesn't happen for me in Chrome.
Thanks for the report on the music. I made some last minute changes to the audio before uploading that may have affected this. Are you playing Standard or Seasonal music? (The default is Standard).
I plan on releasing the full game on Steam, but wanted to gauge peoples interests before moving forward with it. It's probably best to get that set up early, however.
Thanks for your interest in wishlisting it ;)