Rooster comb dark?

[copper2]

I was wondering why roosters combs get dark at the edges?

 

[AtlantisPeeps]

Could be stress, frost bite (Only if you live in a very cold place this time of year) or could be a heart problem. My rooster has the same thing. He's perfectly healthy otherwise so I don't fret about it.

 

[Loriemarler]

I have two roosters in my free range group and it seems they take turns with a dark comb. One day one has purple tips then the next the other one does. The only time both of them have dark combs is when I keep them in the coop and they can't free range. I was wondering if it was liver issues or had anything to do with the feed. They are eating a layer ration with the rest of the flock. I wonder if I should change it to something else