Could you explain this further?
"The hob nail white has a tea stain overcoloring which will wash out and then it will be white white. Use cold water and mild soap predisolved and this may retard this happening. The tea stain like color and sizing may be one and the same, it will wash out with hot if that's your preference."
According to the Homespun website, all of their fabric is woven from untreated, natural (undyed) cotton. White fabric (according to them) is that same "natural" fabric, bleached and then double-rinsed.
Is your experience different than what they are claiming? Also, is the difficulty you're having sewing Homespun due to its inherent elasticity?
Z-Tex has some nice white and natural-colored textures, but the old 50 yard minimum still applies. My samples don't feel as "stretchy" as Homespun.