Each thermistor-LED pair works like this:
1. upon reaching a certain heat threshold the pair's LED lights up, displaying at first Yellow, the lowest.
2. The amount of time and the amount of temperature above the transitionary threshold will determine an increasing value of light as displayed by the paired LED, in this case moving toward Red.
3. As long as the the temperature remains above the threshold, it stays at its max value.
4. Once the temperature is under the temp. threshold, the color slowly attenuates (ideally, in both value and hue) until either it reaches its zero point, or the threshold is again reached.
5. The process repeats when enough heat is again applied to the thermistor.
Construction with micro-controller will involve serializing the inputs of the thermistors and the outputs of the LED through additional electronics, such as the MAX7221 for the LED displays. I have not yet figured out how the grid of thermistor inputs can be serialized.