It's for putting on, e.g. at Lincoln (5)

I believe the answer is:

green

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But I can't explain it at all! Could you help me understand?

(Other definitions for green that I've seen before include "Party label" , "Ecologically sound" , "Eg, avocado, emerald" , "Between blue and yellow in the colour spectrum" , "raw, as > part of course" .)

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