in the 1990's yellow gold lost it's favor to white gold.
in the earlier years of the 1900's, platinum was more popular, albeit more expensive, than yellow gold up until the war years where most brides got plain yellow gold bands when they married.
yellow gold remained popular until the 1990's began to introduce bling to everything.
the other poster is incorrect. natural 24 karat gold is actually a reddish yellow in it's natural unaltered state.
the yellow gold used in fine jewelry is attained by using various alloy metals, just as the other gold colors are attained.
gold comes in white, yellow, rose, pink, green, blue, purple and gray. those colors are achieved by mixing the gold with various other alloy metals. for instance, white gold is a result of mixing reddish yellow gold with nickle, manganese, or palladium. the normal mix that gives us most commercial white gold is 90% gold, !0% nickle. many people are allergic to the nickle in most white gold so either have to use platinum or yellow or rose gold. white gold is not actually white...it is simply in the white spectrum but it's color is actually more of a gun metal gray to very pale yellow to pale pink. the white color is achieved by plating the gold with rhodium, a surface which eventually wears off and has to be replated. that is the major draw back for white gold.
green gold is achieved by mixing natural gold with silver and it occurs naturally and can be mined this way. it was used a great deal by ancient south american indian tribes as it is found naturally occurring there. of course rose gold is made with copper alloy.