There are some great out-of-print knitting books out there, especially in the area of colorwork. Many of them are still available from your local library, or you can pay shocking prices on Amazon or Ebay. But I wanted to highlight some great books that are still in print and don’t cost a fortune.
Sheila McGregor’s Traditional Fair Isle Knitting and Traditional Scandinavian Knitting are both excellent books. They are full of colorwork charts and information about how the traditional sweaters (as well as hats, mittens, and gloves) were constructed. They do not feature lots of glamorous photographs, and they do not contain any line-by-line patterns. They are not coffee table books showing professionally modeled high-fashion knitwear in spectacular settings. Rather, they are fairly highly technical and mostly in black and white, the photographs appear rather dated, and the writing is rather dry. What I love about them is that they give me tools I can use to create my own works of knitting art. They include enough charts to keep me busy for a lifetime, alongside a wealth of information about traditional construction techniques. They leave me free to sort out details of yarn choice and color, to design something that uniquely expresses my own aesthetic, while making use of time-tested techniques and taking inspiration from the wealth of creativity and experience in the Fair Isle and Scandinavian knitting traditions. If you are looking to explore knitting stranded colorwork, these are both books I would recommend.