Passing along (not my post): Update since (check this other link I found: https://socalgis.org/2016/08/01/your-friendly-guide-to-colors/)
There are many tools and websites to find appropriate colors and make a beautiful analytic map. I’d like to share my favorite ones here. You can find the color codes and input it when you modify the symbology, or style of a layer in ArcGIS desktop or online.
For general purposes, you can use https://color.adobe.com which is a part of Adobe software products. You have multiple color palettes and can change the color family to find your favorite colors. If you have a map and you like the colors, you can upload the map as a picture and find the right color codes from your map document.
For analytic maps, ranked features and data, clusters and charts, you can use http://colorbrewer2.org. This website is developed by Pennsylvania State University specifically for GIS purposes. You can change number of classes and see combination of colors, and choose appropriate colors for creating analytic maps, displaying clusters, ranking polygons, and also modifying colors of multiple classes in a chart.
Cartography is the art and science of map making. Choosing sophisticated colors is important to display key contents of a map, chart, or any other document, and also helps the user to find information. If you know other tools, techniques, or websites, please post a comment!