China Prc Sct # 1451 1978 Highway Bridge Color Error

Hi, I wondered if I could get some help with trying to see a price figure for my color error stamp. Any help would be great. I'm willing to answer any questions. The color error is lemon yellow from a reddish orange. I actually have four of these which came from a strip. I haven't seen this particular stamp in lemon yellow,so I believe it is the only 4 in existence. Could be wrong but don't know. I have one in remarkable condition. The other three unfortunately are stained lightly with one having a small paper thin

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It is difficult to tell if it is true color error or just the color faded away.