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

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.

[Rick] chose an Arduino to do all the heavy lifting for the light sensor and activating the LEDs. After a few tests [Rick] got his color sensor working, but it’s not up to par with what he had ...

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.