Came across this early into my metal studies & thought id share, I present to you colored gold! from red to blue purple to green.

Purple a mixture of (about) 20% AL to 80% gold, melting & mixed. It doesnt have any unique property's and as a matter of fact is much more brittle & prone to scratching (then another other alloy listed) & even harder to make ( I however like the color purple & thought it was neat. )

Green is a mixture of (around) 15-20% Electrum (14-30% silver Electrum)  to a 85-80% gold base, Cadmium could also be used but something about health concerns, (also a pain to make and less effective - apparently easier then purple though if I could find a patent id quote them on instructions)

Black is a mixture of 75% gold with 25% cobalt it form a black oxide layer with heat treatment - Copper, iron and titanium can be also used for such effect.

(this is a small list of the colors of gold, ill link my source below if you yourself wanna check
Not to interesting i know but i thought it was cool enough to write about, if you guys know any other cool alloys please share!

Source 1 - https://nancytroske.com/blogs/news/different-colors-of-gold-yellow-white-rose-green?srsltid=AfmBOorlWLZNrmEJQmCKwCEsikIxvK1nsKS0SVuMAarPP0g188akkBQ-
Source 2 -https://patentimages.storage.googleapis.com/50/22/de/a3627232771421/US6929776.pdf (patent owned by a company in Singapore -step by step (vauge) instructions
Source 3 - https://patentimages.storage.googleapis.com/15/10/43/03b591fcefce38/US3067052.pdf

Thank you for reading and have a good day/night
~Ebin H

Other colors i didn't include because i couldn't find a source, but there are rumor of a their being a rainbow of gold to find. (maybe a leprechaun at the end of it?)

Thanks for the share. I hadn't heard of green gold before. There's a pretty good video of a guy called Nile Red on YouTube making purple gold. If I recall correctly you can't work the material at all because of the brittleness/mallabillity. You have to cast it into the final form of the jewelry you want.

I find the electrum part a bit confusing. Isn't electrum already just a mix of gold, a much smaller amount of silver, and maybe a little copper? I remember thinking that it was pretty close to modern alloys around 18k.

I haven't seen much green gold, but mostly it was fairly faint if you didn't hold it up next to regular gold. I've heard (but haven't seen) that it's gotten better and that they use other metals in place of cadmium too.

What I find confusing is the part about 18kt green gold will be greener than 14kt green gold.

It says to add silver, copper and zinc (not sure the percentages). to yellow gold.   

You would think that the more base metal and silver you added would make the alloy greener not the other way around.

Ill look into that youtuber thank you
patents are a pain (and vague), ill search for one on specifically green gold maybe it will point towards something

https://patents.google.com/patent/US6406568B1/en
https://patents.google.com/patent/KR20190131931A/en
two vauge patents & a court case, which means there is another patent somewhere i am unable to find, 
https://supreme.justia.com/cases/federal/us/514/159/
I dont know law but the case reads as follows, which leads me to suspect there is another. unless trademarks dont require patents.... (i dont know im not lawyer)
"Petitioner Qualitex Company has for years colored the dry cleaning press pads it manufactures with a special shade of green gold. After respondent Jacobson Products (a Qualitex rival) began to use a similar shade on its own press pads, Qualitex registered its color as a trademark and added a trademark infringement count to the suit it had previously filed challenging Jacobson's use of the green-gold color."

Note that the patents are not just those lines of words, click download & it will become a pdf in the next tab over where you can read it, (it doesnt download itself unless you manually do it, so no need to worry)

Unless the item, process, etc. is truly unique getting it patented can take decades if you have the $ to get it fast tracked. That's why you see things that have been in production for sometimes centuries with "patent pending" prominently displayed. 

The patent servers used to be fun useful things to surf. You can learn a lot more about how things are made and work by downloading the patent drawings from the device and it's predecessors to compare. I got a good deal on a 50lb. Little Giant power hammer so never built the fluid drive hammer I'd drawn up. Most of the complexity of patented devices is there because you MUST have a minimum of difference from other similar patents and worse they must be an "improvement."

The last time I looked at a patent server it was almost all marketing bloat sending you to commercial sites. It was intensely un-fun trying to find useful info. Without paying that is.

Anyway, unless you plan on selling large quantities of a colored gold alloy you aren't going to run into a patent issue. Most patent suits are intended to make it as expensive as necessary so the one infringing just gives up and goes away.

I doubt strongly, (I haven't looked but still)  doubt colored gold alloys are going to still be under an active patent.

Frosty The Lucky.

    If I recall correctly Nile Red used the vague one from Singapore. He messed it up a couple of times. Trial and error on the really vague stuff until he succeeded. He gives you the formula and procedures that the company was trying to keep a trade secret in that video.