Gold used in jewelry is almost always an alloy, for pure gold would be too soft and as a result not workable and not durable enough for everyday wear.
We mainly use the 18k gold alloy, the standard in terms of durability and look.

Yellow 18k gold is a blend of pure gold (also named 24k gold) and other metals, that will harden the alloy.

18k means that it is composed of 18/75, or 750/000 (75%) gold, and 25% of both silver and copper, which are added for stability.

The 18k gold color is very close to that of 24k gold, with a deep and warm yellow, the only difference being that 18k gold will be much harder and easy to wear (you won't risk damaging the metal as much as you would on 24k gold).

We love using yellow gold in conjunction with dark materials, for its color beautifully complements these tones.