It's not about the color of a crop. The color of the yeast darkens because the green beer darkens over time and stains the cells. Sure, some of the color change is due to aging, but most of the change is due to staining. The only way to know the viability of a yeast culture is to stain it under a microscope. If you are obtaining a lot of organic matter with your crop, then you need to revisit your casting-out and cropping techniques.
Growing a starter from a crop taken on 11/14 is not a major feat. Five to five and half months is not a long time in the grand scheme of things when one considers the number of cells in a crop, even a small crop. I do not recommend it, but I have pitched crops that were that were much older without making a starter.
I am not the only one who has stated that yeast should not be stored outside of beer. Fermentis' parent company, Lesaffre, has an army of Ph.D. microbiologists, biochemists, and biochemical engineers on staff. They are a huge multinational company that handles yeast strains used in a wide variety of applications, including of human research.
Here's what they have to say:www.fermentis.com/wp-content/uploads/2010/07/2010_TT_EN_HD.pdf
"In case of repitching, yeast must not be stored out of beer for long periods, even at low temperatures, as yeast glycogen levels will fall causing slow fermentations."
Additionally, a pH of 5.2 is not low enough to prevent bacteria from growing. The pH has to be taken down to below 4.6 to halt most bacteria, especially pathogens like Clostridium botulinum. The reason why pathogens do not grow in beer is because the pH is below 4.6.
If you consider residual sugars, dextrins, albumins to be major sources of food for wild microflora (most of which will never start because the pH is too low), then you more than likely have never prepared any laboratory yeast propagation media. Have you ever heard of YPD or MYGP? Guess what the "Y" stands for in these media? It stands for Yeast extract, which is the contents of yeast cells (the other part is known as "yeast hulls" after the extraction process has been completed).
We know that rinsing yeast with and storing it under water removes the protective force field that the culture built for itself. Well, it also accelerates glycogen depletion. Guess what happens when yeast cells exhaust their glycogen reserves? They lyse and release their contents into the medium. Yeast extract is far more nutritious to wild microflora than what is left over after fermentation. http://en.wikipedia.org/wiki/Yeast_extract
"Yeast extract is the common name for various forms of processed yeast products made by extracting the cell contents (removing the cell walls); they are used as food additives or flavourings, or as nutrients for bacterial culture media
. They are often used to create savoury flavours and umami taste sensations, and can be found in a large variety of packaged food including frozen meals, crackers, snack foods, gravy, stock and more. Yeast extracts in liquid form can be dried to a light paste or a dry powder."
Finally, the whole rinsing and storing yeast under water thing is misinterpretation of research performed by the ATCC over twenty years ago. That research was conducted to find a means by which to store yeast for long periods of time without the need for refrigeration in countries such as Africa. However, that technique requires all traces
of organic material and nutrients to be removed via centrifudge. The culture that will be stored also has to be propagated under aseptic conditions using absolutely sterile media to avoid the threat of contamination. Finally, the stored yeast has be restarted under laboratory conditions, which makes the method impractical in a home brewing environment. It is much easier for small-scale brewers that lack access to -196C cryostorage to store yeast on subcultured slants. I have maintained yeast cultures on slant since 1993.
Here are a few old photos of my current bank:
The conclusion that all amateur brewers who are serious about maintaining a yeast bank reach is that liquid cultures are not the answer. It's much easier to verify condition and purity when yeast is stored on slant.