Whatkungfuthat if you like the look, try it with a dark brown shade closer to your hair colour rather than black. It can be more flattering. Try to keep it within the width of your natural brow and you shouldn't look like Groucho Marx! I would advise using an eyeshadow and flat angled brush which is also more flattering than using an eyebrow pencil. If in doubt, you could always go to a MAC counter (or similar artist led brand) and ask someone to show you the best shade for you and how to do it with your own brow shape. You don't have to wear a ton of make up to carry them off either, they can look lovely with just foundation, mascara, blush and a red lipstick. Very simple and clean.
If it's done well and suits your style it can look lovely. It does look a bit inconrguous with Coleen's style I agree. Although maybe she's just had them tinted. When you have your browns tinted they put the colour on the whole brow area as opposed to just the hairs and it can initially look a lot darker when you first come out of the salon, and then fades when the dye comes off the skin and fades a little on the hairs.
If you look at Liz Taylor (not now, obviously!) you will see a perfect example of how beautiful this style of brow can look. Or for blonde ladies, have a look, for example, at Madonna in her heyday, to see how good it can look - as well as, obviously, loads of 30s/40s/50s hollywood icons.
The great thing about fashion is there is something for everyone and nothing is compulsory, if it's not a look for you then don't wear it. A great look can be inspired by someone very stylish but copied, not so well, by someone not so stylish so I don't think holding Cher Lloyd up as an example for whether to adopt this look or not is particularly productive.