Welcome to CT. You will get the best benefit by posting correctly orientated, in focus and cropped obverse and reverse of the coin and then any close-ups of the areas in question. The members can't give knowledgable advice without pictures.
Without photos we can only guess and my best guess is the coin in question has turned brown due to environmental issues. If this is the case it's damaged and only worth face value. Welcome to CT.
Quarters do not have a silver coating. It's Nickel Clad. Does it look like this? Then it is just Environmental Damage as stated. I find hundreds like yours Metal Detecting. Exposure to the elements will affect the Clad Layers.
When the clad layer is missing the copper will be very bright. If it looks rusty, it is rusty. Here is a partial where you can see the copper:
