Specifically, let's talk science about gold.
As you probably know, gold is a chemical element (number 79 on the periodic table, represented as Au) that is bright yellow in its natural state, uncommon for most metals. Since its melting point is pretty high (nearly 2000° F, over 1000° C), gold is generally a solid when people see it. Throughout history, it has been prized and considered valuable (the gold standard used to be a common monetary policy, remember?) even before recorded history. (Wait a minute... how do we know that? It wasn't recorded! Ahem. Not the point.)
Gold is neither super-rare nor super-common, but it is easy to handle, easy to smelt, non-corrosive, an unusual natural colour, and relatively non-reactive to other elements. All of these qualities lead to people getting all grabby-hands over gold. Also, it's pretty. I mean, have you looked at a chunk of gold recently? Oooh, shiny...
Moving on. The purity of gold is measured in karats (or sometimes carats, but never carrots), with pure gold called 24k. (By the way, a purity karat is not the same as a weight carat, is definitely not the same as a carrot.) Pure 24k gold is very soft, so for jewellery purposes, gold is usually found in an alloy form, which changes some of its qualities, like hardness, malleability, or colour, amongst other things. Generally, copper or other base metals make up the alloy; the more of the base metals, the lower the k rating for the gold. 14k is probably the most common, and is 58% gold.
The most common "coloured golds" are white gold and rose/pink/red gold.
White gold is gold alloyed with a white metal, frequently nickel, manganese, or palladium. Because of the high nickel content that is probably in white gold, it may be a bad choice for people with metal allergies. (If you’re thinking of getting something made in white gold for someone special… check on allergies first!) The palladium alloys are far more expensive, due to the rarity of palladium.
Rose gold, sometimes referred to as Russian gold (an old term that is mostly obsolete but still crops up occasionally), is generally a gold/copper alloy; the more copper in the alloy, the more red the gold will be. Remember, if the k number is the same, that means the amount of gold stays consistent – the composition of the other metals in the alloy will be what changes, with something other than copper being added in to create a softer red colour.
While there are other “coloured golds” out there, they tend either to be less common, far more expensive, or less appropriate for usage in jewellery due to brittleness or other problems.
Recap! Gold is awesome and highly versatile; because of its value, it was used as money and even now commands a high price. The purer the gold, the higher the karat number. Different alloys give gold a different colour and change its properties slightly.
I’ll leave you with one final fun fact: it has been estimated that if you could collect all the gold ever refined and make a cube out if it, the cube would be 66 feet on a side. That’s a whole lot of shiny.
The Blue Box Blogger sometimes has a strange sense of humour that comes out here rather than the workshop.