Flax is the plant fiber from which linen is made. A distaff is a pole with a notch in the top, from which the strands of flax hang as the housewife, who holds the distaff between her legs, spins the fiber into thread. The natural color of flax is grayish-yellow, and it's stringy stuff. Sir Toby's comparison of Sir Andrew's hair to flax on a distaff is definitely not complimentary.