Yellow of an egg (4)
I believe the answer is:
yolk
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">yellow of an egg</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for yolk that I've seen before include "Part of a 7 Down" , "Food kept by white" , "Yellow (as opposed to white?)" , "something attractive to soldiers?" , "Yellow part of an egg" .)