This articles describes how you can use I2C (TWI) communication, Arduino and temperature sensors to measure 3 different temperatures. It can be very ...

The controlling chip — an Arduino, in this case — can read the intensity of the selected color. The TCS230 uses a 4 x 4 array of photodiodes, along with a Bayer filter.

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.

If you’d like to get more specific, Michael Klements’ Arduino-based scanner lets you quantify colors in numerical RGB values via a TCS34725 sensor.

It's important to have a grasp of how to read Arduino resistors, as they're useful for controlling the current in an electrical circuit.