Please be sure to save the finished tempeh in the refrigerator for leng term preservation (max 48 hours after the competion of fermentation process).
The Rhizopus spp. in the tempeh starter is still alive even after the completion of the fermentation process. So if you leave it at room temperature, the fermentation process will continue and later it can change the color of the tempeh into brown to blackish color.
You may still eat it if the tempeh doesn't have an odd smell or taste. However, after the continuation of the fermentation process, the taste will drops. An astringent taste also tends to come out. So let's not eat it when it has some strong odor which resembles the odor of strong ammonia or alcohol.