This is not a solution to the puzzle, but provides notes from its poser. This type of answer has been approved by the community.
Caution: This post may contain spoilers.
I wanted to do something related to choosing a door from several differently colored doors for a long time. The idea came from a book - The Neverending Story by Michael Ende.
Creative and logistical steps
At the beginning, I considered making clues on the ceiling/floor, but at the end - I discarded them. For the ceiling, I thought of subtly hiding the RGB values (with similar colours - that would be almost undetectable when looked at the picture itself, but with little corrections would be clearly visible). I also thought of making the doors using the same set of numbers for the RGB values. Even though, at this point I had no clear idea what the doors would hide, I chose a set of colors for the doors, and saved the picture. Then I created the ceiling. Since I had no idea what the puzzle would be like yet, I left the images in a folder and let them rest there for a few days.
I had no idea what would be hiding behind each of the doors. I thought: one of them should be safe, the others should be dangerous. But apart from that - no idea. Once the History challenge started, I already knew - the doors would lead to not-so-pleasant history events and the safe one would lead to the present.
Once I had a clear idea, even though I wanted to use pictures in the beginning, having in mind my poor drawing skills, I started writing it as a story, describing every door and what the character sees. Mid-writing I changed my mind - and decided it would be better if I used visuals. So I tried my best drawing them (although it might not seem like I did from the result). At the end, I put all the necessary clues in the walls/doors so I discarded the idea for the ceiling/floor. I even changed the colors of the doors. Basically, nothing was left from my initial creative process.
At this point I needed 3 events that would be sufficiently different from each other.
I first started with fire. Obviously, the door would be red - to symbolise fire. Then I started looking for events related to fire in history - the event needed to famous/big enough. Thus, I searched greatest fires in history. One of the tenth events in a list was the Great Fire of London in 1666 - "666! How well fitting!"
So I decided to use this event and draw a devil to symbolize the number and the fire at the same time - after all the devil is strongly connected to hell and hell is fire.
I had an event with fire, so I wanted the opposite - an event with ice. This led to the light blue colour of the door. So I searched for famous winter battles and Napoleon seemed like a good choice. Then I decided to hide the year in a clock. To make it a little more clear the event happened in the winter, I decided to draw a snowflake. However, due to my poor drawing skills, the snowflake was mistaken for a star and that led to totally different assumption from people. Also, it seemed my clock was not correctly drawn and needed a little nudge. So I changed the second image in the process, fixed the clock and replaced the "starflake" with an asterisk - as it looked more like a snowflake.
I had fire, I had snow, so I thought of something orange/autumn related. However, I couldn't find any distinctive events related to autumn. Not that there aren't any famous ones, but 'autumn' is not really your first thought when you think of them. Then I searched for famous events throughout history, hoping one of them would pop out of the screen and hit me on the head. And suddenly, it happened - the Boston Tea Party seemed distinctive enough and orangish enough on top of that. So now I had to figure out ways to hide the year. I searched the year in Google - nothing interesting. Then I separated it into two two-digit numbers and searched again. The first results were a Surah from the Al-Qur'an. Then I thought there should be some psalm in the Bible that would fit. And there was. So I put the psalm above the door - it seemed fitting enough. Then I decided to put a tea leaf on the door and searched for tea leaves images. I found one that was simplistic enough and on a transparent background. I reduced its size and put it on the door.
This one was the hardest for me. I didn't want it to be green - as green is usually associated to be "safe". And I didn't want to make it too obvious. I had blue, red and orange, so I went for yellow. The door should lead to the present. But 2016 - regardless of how is given, would be too obvious. So I wanted to use a different calendar. I went for the Hebrew one. Now I had to obfuscate the number somehow, but didn't want to use any of the approaches I have already used. I couldn't think of anything creative enough, so I just split the number into two parts and left them on each side of the door. Then I tried thinking of something that could refer to the "present". I thought of putting a drawing of a gift on the door, but that would have been too obvious. Then I thought of using a kanji - but they were used in a recent puzzle and there ought to be people here who knew them, so it would have been too easy. At the end, I figured out the year should be enough.
For the drawing I used mainly Paint and Gimp2.
For the research - google and what sites it led me to.
- Despite the fact that I thought the yellow door was the one with least information, it was solved first.
- Before posting the puzzle, I thought that the red door would be easy to solve, while in fact it took the longest. Perhaps, I should have added some reassuring hints on the image itself.