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Reading http://www.coffeeResearch.org yields the suggestion of manure and phosphate. Note that many USA soils have sufficient amounts of phosphate naturally. http://www.coffeeresearch.org/agriculture/growing.htm
ThanksgivingCoffee.com suggests fertilizer meant for roses, or rose food. To determine what your plants need, test the soil even if you are growing in containers. If you go through your state land grant university, you specify what you wish to grow and results tell you how much of each nutrient you need to correct deficiencies and on an annual basis. So the correct fertilizer is based on your soil condiitons.

I will need to see a photo. This will help me to see the issue. These will normally change many colors from white to dark brown and still be considered normal.

Are you noticing any other symptoms? If this is paired with excessive leaf drop, or spotting, then you might be facing an issue. If not, then I suspect that this is a normal behavior from the trees.

This article will help you care for these: https://www.gardeningknowhow.com/houseplants/coffee/growing-coffee-plants-indoors.htm

Although tap water will be fine, rainwater is always a better choice. Can you include a photo? It could be that it needs to be fertilized depending on how long it has been in the same soil. If it has remained too wet for too long, it could also be a bacterial or fungal infection. A photo would help me better diagnose the issue.

This article will help you with this simple process.
https://www.gardeningknowhow.com/houseplants/coffee/pruning-coffee-plants-indoors.htm

I found this article from Coffee Research: http://www.coffeeresearch.org/coffee/homegrowing.htm

I live in Costa Rica. Just recently I took a tour at a small coffee farm that processed its own beans. We were shown the steps from start to finish. In a nutshell, after picking your ripe (red) fruit you need to remove to outer (red) skin. Then you must clean off the pulp that surrounds the coffee bean itself. Then that bean needs to be dried by sun or a bean dryer. Once you have the greenish, dried bean you can roast it. The simplest way would be in fry pan on the stove but they sell small coffee roasters on Amazon. Since I brew my own coffee each morning after grinding the roasted beans and I can tell you that 20 roasted beans would not be enough to make even a cup of coffee. But you could at least practice cleaning the fruit by hand, drying it and do a sample roast on your cook top. Maybe next crop you´ll have enough for a large batch.