I thought I would share some links with more information. Like any other subject there are different recipes and different ways to do this.
I was given a dye book as a gift a few years ago that I really love: Vegetable Dyeing by Alma Lesch 1970 by Watson-Guptill publications usa. In this book there are several different recipes depending on mordant. She also says to use fresh berries or can dry them for later use. The dried berries according to her recipe gives browns. In her section about general information on dye stuffs she says that berries can be frozen to preserve the dye color when fresh.
Going online I ran into an article by Carol Leigh who is out of Columbia, Mo and has done allot of natural dyeing. This was very interesting reading and I have copied this off for me.
More information here and this one has allot of photos.
I think after reading several articles that the key is to have enough acid in the water and just regular vinegar was not enough acid to get the bright reds. I searched online for the 56% acetic acid- sounds hard to find and pretty strong too. So I went to my go to place for dye stuffs Dharma Trading and found citric acid powder that they said dyers use in place of the 56 % so I just ordered some. (and I just got an order in from them last week-and thought I was set to go-oh well)
I welcome more information on recipes and techniques from anyone that has dyed with poke berries and would like to share.