Short lesson painting numbers are available on every professional brand of paint. It looks like this:
The code of PG7 is Pigment Green number seven. This is Phthalocyanine Green, blue shade.
Learning these codes will help you find the color again in other paint companies and in different mediums. For example, Pyrrole Red is PR255 and PR254 (one is darker than the other), but in Winsor & Newton, for example, their tubes of paint for PR254 is called Brilliant Red. Similarly, the aforementioned PG7 is called Winsor Green instead of Phthalo Green as most companies have it listed under. Now that W&N oil colors are made in France, they have even taken the pigment names off of the back completely and just list the numbers! So now more than ever is a good time to learn the pigment numbers.
Now, there are many colors that fade in the light, otherwise called fugitive or not lightfast, but there is one code that you absolutely have to remember not to buy! This is the code for Alizarin Crimson. PR83. Yes, most old world oil masters and teachers will tell you to buy this color for their class. But look at their older paintings, I absolutely guarantee you that the figures in their pictures have lost all of their blood and look like vampires. Do not buy Alizarin Crimson. While the alternative color Permanent Alizarin Crimson is a bit closer to purple than it is red, it will give you similar tones.