What is the value of a 1941 us copper nickel?

What you have is probably a normal alloy nickel that has discolored over time (the coin actually contains 75% copper). A true mint error where the nickel was minted on an incorrect planchet or blank could be worth from maybe $20-100 on up, depending on condition, but these are very rare and must be authenticated by a reputable grading service such as NGC or PCGS.