Tan is a lighter shade of brown. Occassionally such a shade can be seen on people of caucasian descent who have spent too long in the sun, causing melanin to raise to the surface of their skin to block the sunlight.
Some people have been known to sunbathe to attain this color, though at present times sickly pale skin seems to be more in vogue. Some have even been known to go to tanning salons to achieve this browning color, spending quite a bit of money and effort to promote skin cancer.