How to reuse colors and styles in iOS/xcode?

You can do this by using any singleton class or UIColor extension. Following is an example UIColor extension.

import Foundation
import UIKit

extension UIColor
{
    class func someColor1() -> UIColor
    {
        return UIColor(red: 123.0/255.0, green: 162.0/255.0, blue: 157.0/255.0, alpha:1.0)
    }

    class func someColor2() -> UIColor
    {
        return UIColor(red: 154.0/255.0, green: 143.0/255.0, blue: 169.0/255.0, alpha:1.0)
    }
}

Later you can access the color like

textField.textColor = UIColor.someColor2()

Edit : You can do the same for styles too, using NSAttributedString

class StyleHelper : NSObject{

    class func getSecondaryTextWithString(textString:String) -> NSAttributedString
    {
        let secondaryTextStyleAttributes: [String : AnyObject] = [
            NSForegroundColorAttributeName: UIColor.greenColor(), NSUnderlineStyleAttributeName: NSUnderlineStyle.StyleDouble.rawValue,NSFontAttributeName: UIFont.systemFontOfSize(14.0)]
        let secondaryTextStyleString = NSAttributedString(string: textString, attributes:secondaryTextStyleAttributes)
        return secondaryTextStyleString
    }
}

When you required the style, you will call like

someLabel.attributedText = StyleHelper.getSecondaryTextWithString("SomeText")

Adding on to raki answer extensions of classes like UIColor or UIFont is what I have seen the most of and even though you have to do slightly more typing it is the equivalent in iOS.

extension UIFont {
class func myFont() -> UIFont {
    return UIFont(name: "HelveticaNeue", size: 22)!
}

class func otherFont() -> UIFont {
    return UIFont(name: "Arial", size: 22)!
}

}

Another thing that might be relevant coming from android is the equivalent of a strings file in iOS programming since you seem to be interested in reusing these styles. For strings:

and then fill in strings you are going to use in your app

"ACTION_CELL_MENU" =                "Menu";

Then in your code elsewhere

label.text = NSLocalizedString("ACTION_CELL_MENU", comment: "")

Pretty old question, but you can actually add any color to Assets.xcassets, just call context menu on the list of resources, then "New Color Set" and done! You can use it with Interface Builder or programmatically.