Kernel size, hull thickness and pigment content differentiate yellow corn from white corn. As a general rule, the thinner a kernel's pericarp, or hull, and the less carotene it contains, the whiter the kernel appears. The taste difference between white and yellow popcorn is negligible -- they all contain the same starch inside -- but some varieties, such as Baby Rice and Baby White, are more tender because they have thin pericarps.
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Whiteness Varies With Variety
Popcorn kernels vary in size according to variety. On the small end of the scale, the rice-like Japanese hulless has a pericarp so thin it appears transparent, and you can see the starch lying beneath. On the large end of the spectrum, regular movie-theater popcorn has a thick pericarp packed with orange carotene. In between are numerous heirloom varieties, such as Baby White, Baby Yellow, Ladyfinger, Little Indian and Baby Rice, whose color falls in between Japanese Hulless and regular popcorn. As a general guideline, if you want white, delicate popcorn, look for any variety with "baby" in its name.