I was just searching for an online tool to help pick a website color and entered "color picker". Instead of just a bunch of search results, Google presented its tool, which was perfect for my need. Just move the slider left and right to move through the spectrum, or enter your specific values.
At the bottom of the image below, you'll see the probably familiar RGB (Red-Green-Blue) and CMYK (Cyan-Magenta-Yellow-blacK), but also HSV and HSL, both unfamiliar to me. HSV is short for Hue-Saturation-Value and HSL for Hue-Saturation-Lightness and these alternatives are explained in detail at this Wikipedia link.