The book touts itself as covering basic sigil magic, which it does do within the first few chapters, between introducing Austin Osman Spare's method of sigil creation and listing a few others. This beginning foundation was quite helpful and thought-out, but somewhere along the way it seemed as though the topic of sigils were not purely enough to fill the book, as the chapters covering specific colors could have been insightful in another setting that was not intended solely for sigil magic, which is not to say that colors cannot be integrated into sigil work, but that the book's title can be misleading in that manner.
There are beneficial takeaways from this book, but keep an open mind into your own correspondences of certain colors and your own beliefs that may or may not include a deity or deities as you progress through it.