Make a mason jar mood lamp. via instructables
This is a dark activated color changing mood lamp. Its brains is a ATtiny85, but you could also use an Arduino.It has a light sensor which sense the light condition and decide when the room light is turned off.This then will light a RGB LED and slowly fade through different colors.
The brain of the lamp is Attiny85. The LDR and 10K resitor makes the light sensor.The sensor output is connected to the attiny analog pin-3.The sensor detect when the room is dark and tell attiny to give varying pwm signals to the RGB led.According to the different values of PWM signal the color of the RGB led changes.For power switch I used a sliding switch.