Well, you were not the first. A scientist named Ranvier reported differences in muscle color within and among species back in 1873. The explanation for the color differences is pretty simple and has a basis in physiology. Most animals have some combination of these two fiber types, though the destinctions may be less obvious. This gives them a darker, reddish color.
Humans also have dark and white meat.
Some of our muscles, like the soleus in the lower leg are almost all slow twitch fibers. Others such as those controlling eye movements are made up of only fast twitch fibers. Function dictates form in these highly specialized muscles. The majority of human muscles contain a mixture of both slow and fast fiber types. From an evolutionary standpoint this makes sense.