image/color: documentation doesn't include links to relevant color theory resources

[dolmen]

What version of Go are you using (go version)?

$ go version
1.13.7

Does this issue reproduce with the latest release?

Yes: https://tip.golang.org/pkg/image/color/

What did you expect to see?

The image/color relies on some color theory. But no pointers are given to learn about that theory.

Here are a few questions for which the documentation should give answers or even just hints:

• What is Alpha?
• What is the difference between alpha-premultiplied and non-alpha-premultiplied (some answer exists in doc for type RGBA, but more in overview would be helpful) and when should one be used).

Also, no examples. That would be useful to understand Model.

What did you see instead?

The package overview section is a single sentence:

Package color implements a basic color library.

[dmitshur]

There were some old blog posts on image packages at https://blog.golang.org/go-image-package and https://blog.golang.org/go-imagedraw-package that have additional relevant information. Perhaps linking to those is a good idea.

/cc @robpike per owners. Also /cc @nigeltao.