These college-level texts are drier than three-day old toast, but who am I to keep you from them? If you like that sort of thing, go for it.

• Chandrasekhar, S. Newton's Principia for the Common Reader. Oxford: Clarendon Press, 1995.
  • Thorough, yet somewhat complex and a bit of a snore.
•  
• Hall, A. Rupert. All was Light: an introduction to Newton's Opticks. Oxford: Clarendon Press, 1993.
  • Yet again, not for the faint of heart. Only read it if you have slogged through Opticks and still want more punishment.
•  
• Sepper, Dennis L. Newton's Optical Writings. . New Brunswick, NJ: Rutgers University Press, 1994.
  • Again, only if you want more academic-speak punishment. I like this one a little bit better because it is short. And has slightly less arcane speech.