From Knitting New Scarves:

For this achromatic scarf worked in Intarsia, white stitches peek out of “windows in a light and dark gray fabric (see front view at left and back view on page 77). If you’re new to Intarsia and would like to use the alpaca recommended in the pattern for the scarf, I suggest swatching with some scrap yarn first. The alpaca shown here is wonderful but it doesn’t weather ripping out well, so isn’t the best choice when you are first learning.

Requires US 15 straight needles and one US 15 double-pointed needle.