From what I remember, it is a way for telling them apart since there's so many different types of pills, different manufacturers, off-brand vs on brand medications, etc. If you look at a pill bottle (at least my pill bottles have them) there's a descriptor box that describes the size, shape, and color of the meds inside so it's harder to mix them up with other things. Not to mention the amount of dosage for each medication differs, the engineered coatings for different types of meds change things too, the surface area required for the most effective release rate; each type of pill is as unique as possible for their own reasons