For painters, creating fine art, you should find the Munsell Notations given here to be more than accurate enough!
Measuring the color of a paint is a tricky topic. As an artist you've probably figured out that paints can look different depending on how thick they are applied. Lighting can also affect the perceived color of a paint, not to mention wet vs. dry, the angle of the light source and so on. This is the problem in trying to catalog the colors of paints. Different people use different tools and standards by which they measure the paints. Some sources of Munsell Notations are probably better than others but all should give you a very reasonable idea of a color's hue, value, and chroma.
Williamsburg paints for example, has a very controlled and repeatable procedure for calculating Munsell Notations. Williamsburg Paints uses equipment to ensure that the paint films are precisely 6/1000 of an inch. According to Williamsburg, this is considered an opaque mass tone. They then dry the paint and take a color reading of the paint film using a high-end spectrophotometer.