There is a lighting bug in 1.7.x where everything seems darker.
This bug is most noticeable in the nether where there is no clear sky,only darkness.It also is noticeable a bit when the player goes under a tree,the view changes to as if it were on the "moody" brightness setting.
I have checked my settings and i can assure you that the brightness is all the way up and my render distance high
Duplicate of MC-31681.