Answer: Based on your description I would not have guessed red thread -- red thread normally occurs in cooler weather and affects lawns that are stressed, especially by low fertility in combination with other factors. And, you would have seen distinctive pink or red "jelly" on the lawn. Here is a description of it.
The symptom of black could have been spore release by a smut -- another cool season problem connected with low fertility. In this instance it is more of a powder that you might notice on your shoes, not really a sheen.
However, it is very difficult to make this type of diagnosis long distance. You might be able to diagnose it using the following information from the University of Maryland.
But, I would strongly suggest you consult with your local county extension to obtain a specific diagnosis of the problem. They will probably need a sample as well as overview photos of the lawn to see the pattern of discoloration or death. Based on knowing that specific diagnosis, you can decide how to treat it if necessary. If a chemical control is needed they will have the most up to date information on what to use and how/when to use it for maximum results.
They should also be able to help you with a lawn maintenance plan to assure you are fertilizing and mowing correctly and minimizing stress so it will be less susceptible to pest/disease problems.
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