Final answer:
The maize kernel phenotype becomes variegated due to the insertion and later excision of the Ds element in the gene coding for red pigmentation, resulting in kernels with red spots or streaks.
Step-by-step explanation:
The maize kernel phenotype when a Ds element jumps into a gene coding for red pigmentation early in development, and then later jumps out, would be variegated. This variegation occurs because the Ds element causes chromosomal breakage at the Ds locus, which inactivates the C' allele and results in patches of cells with no red pigment. When the Ds element jumps out in later cell divisions, some cells can revert to synthesizing the red pigment as directed by the unbroken C' allele. The result is a kernel with spots or streaks of red color on a colorless background, a variegated appearance.