Just as cashmere is best in the cold, linen makes the most useful knitwear for the moderate temperatures of spring and early fall. Just porous enough to breathe when it is knitted properly, linen is another of those handy fabrics that wear cool when it is warm and warm when the temperature cools.
Like cashmere though without much of the expense, linen can be dyed a variety of colors. The ones that suit it best are natural tones, particularly greyed blues, soft, moss-like browns and greens and, well, natural. Wear it in crew neck form or as a to-button cardigan that works as a jacket but, please, for humanity's sake, eschew zippers and remember that vee necks are meant to be worn with neckties.
The examples in the photos are from Ireland's Inis Meáin Knitting Company.