It is the strength factor of the gold such as 10 karat or 14 karat 24 karat is the strongest but may reflect color changes as well I personally like 14 karat. I worked at a gold plant inside...
$1188.32 per Oz on 03-Aug-2010
A US 1911 $5 gold coin is 90% gold & 10% copper which is 22Kt. gold.
24K Gold Purity - 100% 24K Gold Purity - 75% 14K Gold Purity - 58.33%
White, yellow and red.