Hello,
You’re right to think about when to change colors for a smoother transition. Changing colors on a predominantly knit row can indeed make the seam less noticeable, cat noises as the knit stitches on the front side of the fabric can help hide the color change.
In your pattern, it sounds like the designer is asking you to switch colors on a purl row (Row 19) to achieve a specific texture or design effect. Purl rows can be more visible than knit rows, especially if you’re working with a color change. The seam might be a bit more noticeable, but it could also be part of the design, especially if it’s intended to create a specific look or texture.
Best Regards