Your 1975-D is a little banged up, but if you need it for your date set, keep it until something better comes along. If you're wondering if it's valuable, it's not. Go ahead and spend it
Your title states 1971 for the 1975 you are showing. Make sure to check your title for accuracy before posting.
That would be normal environmental toning.. Many Cents turn brown after many years of circulation and exposure to the elements.
Redish would be some chemical that was previously used. Such as paint which wears off slowly over time. It is not any kind of mint error.
Both are Clad Quarters. They look like normal circulation wear. Face value. Last year for silver planchet Quarters was 1964.
