Define a global color

You should create a category, not a subclass. This will extend the UIColor class, and add your colors to it.

.h

#import <UIKit/UIKit.h>

@interface UIColor (CustomColors)

+ (UIColor *)myColorLightGreyBGColor;

@end

.m

#import "UIColor+CustomColors.h"

@implementation UIColor (CustomColors)



+ (UIColor *)myColorLightGreyBGColor {

    static UIColor *lightGreyBGColor;

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        lightGreyBGColor = [UIColor colorWithRed:241.0 / 255.0 
                                           green:241.0 / 255.0
                                            blue:241.0 / 255.0 
                                           alpha:1.0];
    });

    return lightGreyBGColor;
}

@end

By defining your colors this way, and #importing the category, you can apply this custom color the way you were already trying to.

How about a macro?

#define DEFAULT_COLOR_BLUE [UIColor colorWithRed:.196 green:0.3098 blue:0.52 alpha:1.0]

Put it in your appname_Prefix.pch file or more likely a header file included in your prefix file

And it will be like:

cell.backgroundColor = DEFAULT_COLOR_BLUE;

Your class name is lightGreyUIColor

Hence you need to use it as

cell.backgroundColor = [lightGreyUIColor lightGreyBGColor];

Or you need to create a category on UIColor.

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EDIT:

Your code [UIColor lightGreyBGColor] tries to search for the method in UIColor itself, however you have subclassed UIColor by lightGrayUIColor.

As you are calling, it looks like you intended for a category.

Side Note: ClassName should be captial as LightGreyUIColor.