You can throw a Raspberry Pi camera and OpenCV at the problem and approach it through software, or you can buy an off-the-shelf RGB sensor and wire it up to an Arduino.

We’d seen it done with buttons, switches, gestures, capacitive touch, and IR remote, but never like this. [electron_plumber] made an LED that can be blown out like a candle, and amazingly it … ...

Here is a tested Arduino project that uses 3 sensor probes as water level indicator with 3 leds and one LCD display + a simple controller that turns on a motor when the water has reached the desired ...

The Pressure Sensor Module incorporates a material called Velostat with the Arduino. This material adds more resistance when more pressure is applied to the material. This module also uses the RGB LED ...