In Fair Isle knitting patterns, new yarn colors will inevitably be introduced. That’s the nature of Fair Isle knitting!
How should you begin knitting with a new color?
There are many ways to do so, including the following four options.
Option 1:
At the beginning of the row, simply pick up the new color and begin knitting with it. You can leave a long tail, then later on, after the knitting project is completed, re-visit the yarn tails and weave them in with a darning needle. When finishing yarn tails with a darning needle, always attempt to disperse your woven tails so the weaving is evenly distributed (and not concentrated in one area).
Option 2:
When I worked at the Shetland Textile Museum, I noticed many (though not all) Shetland knitters introducing a new yarn color by simply tying a square knot with the new yarn color and the existing yarn color. Then, once the knitting project was completed, they would cut the tails short, without weaving in the ends. Their justification in doing so was based on the central nature of Shetland wool, its “sticky” texture that ensures the yarn will remain intact and secure.
Option 3:
For a neat appearance and smooth transition to a new color, weave in (or knit in) the new yarn an inch or more before the beginning of the row. That way, the new yarn color is already woven in and secured by the time you reach the beginning of the row. This ensures there are no holes at the beginning of the row.
Option 4:
Splicing yarns is one way to introduce a new yarn color into your knitting. The benefit of splicing is the avoidance of knots and potential bulk. I believe that splicing yarns creates a smoother, finer, more seamless finish to the garment. This is my go-to method for introducing a new color in Shetland wool.