Rods and cones
Rods and Cones are the sensory cells in the back of your eye that detect light.
Rods
Rods sense only light intensity, not color. They sense edges more sharply than cones. If you are outside at dusk, you may feel a sudden switch of your vision from color vision to black and white, this is your visual cortex switching to only rod input when cone input isn't working as well in dim light.
Cones
These are the cells that detect color in your eye. There are three different types of cones that respond most strongly to three different wavelengths of light. Your visual cortex takes the combined response of the three types of cones and makes up the blended color in your mind. Magenta for example is an imaginary color. It's the color your brain makes up to explain why both short and long wavelengths of light are detected, but not the wavelengths in the middle. Most colors are on the color spectrum you learned in school (Red, Orange, Yellow, Green, Blue, Indigo, Violet), and will trigger a single cone type, or two adjacent cone types.