Accept #abc, abc, #aabbcc, or aabbcc and return a lowercased #aabbcc. Three-digit hex is expanded by doubling. Returns null on anything else.
#abc
abc
#aabbcc
aabbcc
null
Accept
#abc,abc,#aabbcc, oraabbccand return a lowercased#aabbcc. Three-digit hex is expanded by doubling. Returnsnullon anything else.