Try this:
UIPageControl *pageControl = [UIPageControl appearance];
pageControl.backgroundColor = [UIColor clearColor];
You can play with Alpha too:
[[UIColor alloc] initWithRed:0.0f green:0.0f blue:0.0f alpha:0.7];
So, the statement would become:
pageControl.backgroundColor = [[UIColor alloc] initWithRed:0.0f green:0.0f blue:0.0f alpha:0.7];