I've found color charts handy lately. Usually it's for the foam fingers. A customer asks for hot pink...what exactly is hot pink? Well, it's a question with no exact answer, but it's useful to have a starting point.
These are two sites I've found and used. Lots of colors, and it's nice that the colors also have names on these charts. Hot pink, for instance, or popcorn yellow.
Yesterday, a customer asked for Detroit Lions colors and I came across this color reference for all of the NFL football teams. It's interesting to see how some of the teams have primary colors...and additional colors...and alternate primary colors...and face mask colors; then some just have variation in their accent color -- it can be metallic silver, or non metallic, or white. Most at least have two colors and white, except the Jets and the Colts. Green for the Jets, Royal Blue for the Colts. White. Period.
What's your starting point for choosing colors? Color charts? A photo? Do you just get in there and start moving sliders around?