If you have been doing development for a while, or just find yourself design challenged, there are shelves of books you can pick up to help you understand key principles. Some are better than others - where does The Principles of Beautiful Web Design by Jason Beaird stand?
This is an easy read - most people should be able to complete it from cover to cover in about five hours. Visual examples help break up the flow of information. Additionally the headings are designed to make scanning for a particular section easy.
Because it isn't a dense book (in either content or length) this is more of a survey of design principles rather than a reference. Broken down into five sections, it covers layout, color theory, imagery, texture, and typography. Each one is given enough discussion to get you thinking about it. Tying it all together is a narrative about a specific site which he takes from design to implementation.
A broad survey
If you are looking for an in depth explanation this book will not help much. Instead it focuses on exposing the interested designer to different approaches. You won't come away from this book with a narrow view of visual design. Instead it will challenge you to question whether your current site should use a fixed grid, a fluid grid, or embrace responsive layouts. It won't prescribe a killer color scheme but instead points you to resources to help you figure out what would work best.
One minor thing that would have been nice with this approach would have been to include pointers to other books. Interested in typography? Here's a couple other books to read. Maybe that can be explained away as a "feature" of Sitepoint wanting you to stay in the family. Whatever the reason I enjoy it when authors give you a trail to follow.
The perfect hand-me down
If you are a developer looking to make the transition to front end development this book is a good resource. If you already have some exposure to color theory or the other topics covered then it might not be as helpful. Unlike those invaluable dog-eared books on the shelf The Principles of Beautiful Web Design is the sort of book that will set you on the path to creating better experiences. Although you won't be doing so this is still one of the better Sitepoint reference books.
Assuming you come across a good deal I would not hesitate to recommend buying a copy. Once you are done you can pass it on to other developer friends and help encourage a richer and more thoughfully designed web experience. One by one we can help make the Web a slightly more pleasant place to browse.