Rules of ink colour I learned long ago:
Black for adults,
Blue for schoolkids,
Red for teachers,
Green for ransom notes and conspiracies.
I use red for taking off points on exams, and green for giving them back when regrading.
After a nasty experience several years ago, I began using green to number my exam copies before giving them out and purple to (separately) number them when they are turned in. For large classes (40+ students), it makes it easier to keep track of how many students showed up for an exam and how many of those actually turned their exams in. 
What about brown? I have a brown Pelikan pen that I fill with brown ink.
Also, I believe the chief if MI6 uses green ink.
Well, shit… 
I am not remotely surprised.
(see rules above)
Back during COVID isolation, I played around making quill pens (no shortage of geese hereabouts). During one of the few outdoor meetings with my granddaughters, I gave them one each.
For monks and traditionalists.
There were lots of walnuts lying around that fall, so I picked up some husks and boiled some down to make walnut ink in the simplest way possible.
I wrote my granddaughters a letter, folded into itself and sealed with wax, Jane Austen style (no envelope).
(The red block is downhill ski wax.).
Amazingly, it survived Canada Post and arrived in good condition.
A couple of weeks later I got replies. They had made their own batch of blueberry ink and written back.
So if my Gen Z granddaughters play @sqlrob’s game of Never Have I Ever, they will have to admit that they have received and sent letters written with a quill pen.
Now I have to know: is there difference between downhill ski wax and cross country ski wave?
and wax for brazilians?
I don’t know about their actual composition, but they are used differently. Downhill wax is chosen for maximum speed given the temperature and snow conditions. X-country wax is applied for slipperyness (glide) in the same way over most of the ski, but chosen to grip the snow (kick) for a section under the foot.
By colour convention, red X-country wax is softer and stickier than red downhill wax, totally unsuited for sealing letters.
Brazilian waxing has not been shown to improve ski performance. However Lucas Pinheiro Braathen has come out of retirement so who knows?
Did you have to boil it outside? Does it have a strong aroma?
Not that I noticed, but I wasn’t about to risk splashing it about the kitchen. That stuff is permanent.
I got really into fountain pens for a while but I always hated refilling them, and cartridges were not always reliable.
But Pilot Varsity disposable fountain pens are pretty great. I know to some folks that’s heresy 
I really like the design of Lamy Safari/Al-Star/Vista pens, and have been using rollerball ones. But Lamy ink is pretty mediocre. Morning Glory Pro Mach is a great pen though…
The only useful thing I learned from the deluge of unsolicited mail from probate lawyers, is using blue ink to sign documents shows which are the originals and which are copies.
I like using purple pens, and green ones.
I support your Varsity usage.
At work I’ve been using a JPG (colour scan) of the squiggle that vaguely looks like the short version of my signature done in blue ink on everything that comes out of a computer since 2002.
In all of that time exactly two people have asked me about it.
Heh, I get to use green ink (for pens and rubber stamps) at work for certain documents.