I have done something very similar in the recent past; the application requires a variety of user-selectable color schemes.

Topic

Create a theme class with properties for each of your color types. Try to avoid describing the specific use of ( submitButtonBackgroundColor

), instead describe the purpose (this way you will end up with far fewer color definitions):

extern NSString * const ThemeChanged;

@interface Theme : NSObject

+ (Theme *)currentTheme;
+ (void)setCurrentTheme:(Theme *)theme;

@property (nonatomic, strong) UIColor *backgroundColor;
@property (nonatomic, strong) UIColor *foregroundColor;
@property (nonatomic, strong) UIColor *darkerForegroundColor;
@property (nonatomic, strong) UIColor *lighterForegroundColor;
@property (nonatomic, strong) UIColor *highlightColor;

@end

      

        
        
        
      

    

Implementation:

NSString * const ThemeChanged = @"ThemeChanged";

static Theme *_currentTheme = nil;

// Note this is not thread safe

@implementation Theme

+ (Theme *)currentTheme {
    return _currentTheme;
}

+ (void)setCurrentTheme:(Theme *)theme {
    _currentTheme = theme;

    [[NSNotificationCenter defaultCenter] postNotificationName:ThemeChanged object:nil];
}

@end

      

        
        
        
      

    

This class can then be created with each of your desired schemes (one for the day, one for the night).

Each of your view controllers must access to [Theme currentTheme]

receive colors. They (your view controllers) can also register themselves as a notification watcher ThemeChanged

to dynamically update their view colors if theme changes with setCurrentTheme:

.

Day / Night Definition

As for the automatic update based on the time of day, you can use a recurring one NSTimer

at a reasonable interval, check the current time and call setCurrentTheme:

that dark theme object that you created.

@interface DayNightHandler : NSObject
@property (nonatomic, strong) NSTimer *timer;

@end

@implementation DayNightHandler

- (instancetype)init
{
    self = [super init];
    if (self) {
        _timer = [NSTimer scheduledTimerWithTimeInterval:1
                                                  target:self
                                                selector:@selector(checkTime)
                                                userInfo:nil
                                                 repeats:YES];
    }
    return self;
}

- (void)checkTime {
    NSDate *currentDate = [NSDate date];
    NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitHour | NSCalendarUnitMinute
                                                                   fromDate:currentDate];

    NSLog(@"%@",components);

    // Very crude
    if (components.hour >= 18 || components.hour <= 6) {
        // set dark theme
    } else {
        // set light theme
    }
}

@end

      

        
        
        
      

    

You might want to trade the day / night check for something more solid, this is just a high level example to help you on the right track.