I couldn't change only the purple background where the numbers were, so I had to change the whole nav bar color so it would apply to the background of the numbers:
- (void)setNavBarColor:(UIColor *)navBarColor titleColor:(UIColor *)titleColor {
[[UINavigationBar appearance] setBarTintColor:navBarColor];
[[UINavigationBar appearance] setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:
[UIFont fontWithName:@"Futura-Medium" size:17.0f],
UITextAttributeFont,
titleColor,
UITextAttributeTextColor,
nil]];
}