Frostbite On Combs

[Chicklette 1]

I have 2 hens that have large combs and wattles and I have been putting vaseline on them every other day or so. It is 15 degrees here in KY. and although they still like to go out into the pen, I have noticed a small black spot on one of the combs and the color becomes pale on the other one. These hens are the ones that are both laying so far for me even with the limited light. Is there anything else I can do for the frostbite issue? Should I put the vaseline on every day without fail? I can't imagine it would hurt. Any additional suggestions aside from knitting them bonnets would be appreciated.
Strange also is that my sikie couple like to be outside almost more that the other girls and I thought they did not handle cold weather as well as chickens with more closely packed feathers. Any one else notice that?

 

[Caseman]

I raise Bantams and they love to go out.. I don't bother putting any thing on their comb. I got 6 coops and befor I open the coops you can hear them in there singing-soon as I open that door out they come to get fresh water and feed- I let them out at 9:30 today -their feed and water is outside - I feed 2 times a day with Black sun flower seeds & whole corn in between feeding..they love the cold weather

 

[Miss Lydia]

I do use vaseline on my roosters combs and when it's down in the low teens and twenties they get it rubbed on everyday. also I use Bag Balm