Finally, we're at the singular leaf of the incredibly lopsided tree.
There are two major frameworks for the way color works. They are not conflicting scientific interpretations or anything, they just govern different mediums and are both correct. These are the ADDITIVE and SUBTRACTIVE systems.
In the additive system, the primary colors are red, green, and blue. As such, it is also known as the RGB system. It governs the color mechanics of light on its own, and is what computers' color systems are built around.
In the subtractive system, the primary colors are cyan, magenta, and yellow. As such, it is also known as the CMY system. It governs the color mechanics of solids and liquids, like paint, ink, and other mixable physical vessels of color.
For our purposes here, "primary colors" means the set of colors you can combine or leave out in some ratio to produce every other color.
All colors can be notated as 0-100 percentages of the primaries of either color framework.
Orange has 100% red, 50% green, and 0% blue; or 0% cyan, 50% magenta, and 100% yellow.
Cyan has 0% red, 100% green, and 100% blue; or 100% cyan, 0% magenta, and 0% yellow.
The final difference between the additive system and the subtractive system, and the one that lends them their names and their necessity of separation, is what happens when a color has more than 0% of all three primaries. In the additive system, the color gets lighter (by the amount of the color with the lowest percentage as a ratio of the highest color, but you don't need to know all that right now). In the subtractive system, it gets darker by that amount instead. If you were to ignore this rule, there would be no reason to have two systems; we would just be doing the other one for funsies, which would be dumb and pointless, but I've had people I explain this to in real life just miss that part and assume I was making them do twice as much mental work for no reason for a week (the longest someone has ever listened to my color ramblings). There is a reason for everything I will do and say here; if you didn't get this from the introduction, I take this very seriously. Also, since I don't know where else to say this, equal percentages of everything are always grayscale.
White has 100% red, 100% green, and 100% blue; or 0% cyan, 0% magenta, and 0% yellow. Think of it like this: a bunch of different-colored lights shining at the same spot will produce a brighter color than if any of the lights were shining alone; and a piece of paper with 0% of any ink on it is just white.
Black has 0% red, 0% green, and 0% blue; or 100% cyan, 100% magenta, and 100% yellow. Think of it like this: if there is no light at all in a room, it's just black; and if you completely cover a paper in all colors of marker, it'll get darker and darker until it's too dark for any effect to happen when you draw more.
Light orange (75% luminosity) has 100% red, 75% green, and 50% blue; or 0% cyan, 25% magenta, and 50% yellow.
Dark orange (25% luminosity) has 50% red, 25% green, and 0% blue; or 50% cyan, 75% magenta, and 100% yellow.
That concludes the material of lesson 1. Before you go to the next one (which, if you're reading this parenthesis, doesn't exist yet), try to let yourself absorb the knowledge rather than speedrunning it, maybe read it again later to benefit from the spacing effect. It's better if you take just a little bit away from this than if you binge-read every lesson and remember nothing in a week. Have fun.