Final answer:
An obvious difference between two colors along a hairstrand, due to variations in melanin distribution or hair coloring practices, is known as banding or hair color variegation.
Step-by-step explanation:
An obvious difference between two colors along a hairstrand is referred to as banding or more technically, hair color variegation. This occurs when the distribution of melanin, the pigment that gives hair its color, varies along the length of the hair. This could be due to natural genetic factors or as a consequence of hair dyeing practices.