Kohaku

Regarding the usage of Kohaku in Japan, according to the first source below, there were only 7 people (2 こはく, 小白 and 琥珀 & 1 古白) with this name in phone book records, which is 0.00002% of the recorded population in these records.

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In the early 1990s, it started to become more often used (by 2003, 21 / 0.016% of boys and 18 / 0.015% of girls have that name), though it was still rare at that point, and before 2002, according to the second source below, the gender of the name tends to be slightly feminine.
Interestingly, none of the Kohakus in the data from 1989-2003 have the kanji used to mean "amber," instead using other kanji that can be made into Kohaku (like 瑚伯, 虎白 and 湖葉玖), but there is one child actress born in 2005 who has the kanji used for this particular meaning (her name is Kohaku Suda / 須田 琥珀), so I think that it was only in the early to mid 2000s that 琥珀 began to catch up.

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Sources: www.douseidoumei.net and www.namaejiten.com (data on this particular source not a full representation of baby names being chosen in Japan from 1989-2003).

Kohaku is also a male name!

Kohaku has been used as a masculine name.