You can also go to the Vallejo site and look at their catalog.
Most online vendors like Scalehobbyist and Squadron use the full color number broken down by paint line and type, Sprue Brothers uses both the full number and just the last 3 but organizing by paint line.
Then there is this handy free app called Hobby Color Converter that lists many different manufacturers, their paint lines, color swatches and catalog numbers. It's constantly updated and improved.