Controlling an RGB LED color range from an analog temperature sensor (no Arduino, etc.)
The simplest analog circuit I can come up with is this:



V1 represents the temperature sensor output value.

The values of R1 and R3 may need to be adjusted specially if you use other transistors (you can use variable resistors to find out the correct values then replace them with fixed value resistors).

You may also need a voltage divider on the base terminal of Q1.

This is the output signal analysis.



This assumes you are using a common anode RGB LED.