NEED BROWN OR BLACK ICING?   For brown icing melt 
unsweetened chocolate and mix it into your white icing.  It's not only brown, 
it tastes great too!  For black icing, just add black gel coloring to your brown icing.  
You'll use less black coloring and the icing will taste like chocolate! 

THE SECRET TO DARK RED ICING  Making dark red 
icing can be a challenge unless you know the secret.  Make your icing a day
  ahead of time.  That dark pink icing will darken over time and turn into the 
red you need if you give it 24 hours.  I like to make my red icing using maraschino 
cherry juice as my liquid.  This turns my icing a nice pink then I don't need as much 
red food coloring.  Add some almond flavoring and your icing will taste WONDERFUL!

Royal Icing Recipe