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.

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

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.

Ever thought of using touch sensors on your projects but didn’t because it would be too much work? [Paul Stoffregen] proves that it can be pretty easy if you use the CapSense library for Arduino ...