If you missed the tips at the bottom of my first post, check it out, there's some good stuff in there!!
This post is a refresher on color theory. I wrote this to refer back to it later.
In the RGB model, colors are a combination of hue, saturation, and value
Hue is the base pigment or wavelength: 
Saturation is the depth of the pigment: 
Value is the relative lightness or darkness: 
Tints are when you add white to a color, tones are when you add gray, and shades are when you add black
Color harmonies such as the monochromatic, complementary, and triadic color schemes give us a better idea of how colors can work together. The harmonies reach their full potential when you factor in saturation and value. You can get a better feel for them by playing around with this:
https://color.adobe.com/create/color-wheel
Color harmonies help inform our use of palettes. You can create your own with the color wheel above, or explore some below:
But we're not done yet. Once you find yourself a banger palette in RGB, you can turn it into a text gradient... or even a block palette!!
Text gradients (for nicknames, signs, MOTD, MiniMessage, etc):
Lucid's RGB Gradient Generator for MC
RGB Gradient Creator
Block palettes - including multiple block options, and even suitable decoration blocks:
If you don't have a talent for it yet, the block palette tool helps you identify blocks with similar colors, which aids in creating more natural gradients and, assuming you use them right, avoiding randomization. You unlock a world of possibilities when you start thinking about blocks purely in terms of their colors rather than what they're supposed to represent. I encourage you to experiment with the decoration blocks as well to add texture!!
Next, I would like to talk about accent colors. The snobs that design real-life houses for a living have a tip called the 60-30-10 rule. The point is to maintain the balance in a space by following a ratio for your use of colors and/or patterns. Consider roughly three colors.
60% of the space gets taken up by your main color: typically the walls and floors.
30% of the space can be another color, typically contrasting in some way. This shows up on accent chairs, curtains, furniture, and feature walls.
10% of the space, give or take, is composed of your accent color(s), which shows up in cushions, lampshades, artwork, plants, or other decorations.
Check out this sick-ass room:
The composition of the photo flips it around, but most of the room is white. Probably, anyway. Contrast that with our 60% color, black. The yellow sofa and table frame complement the analogous blue accents. The blue only pops so well because of the sparse use of color otherwise, and the layout of the room ensures the light catches the accents favorably.
But hold the phone, either that's at least four main colors or I've lost my god damn mind.
To use more colors without disrupting the balance, start small, and use color harmonies as accent colors. Hear me out:
This space is mostly made up of white and off-white. We can use tints, tones, and shades without disrupting the balance because it's essentially adjusting a value slider. And our accent colors, introduced in small doses, follow an analogous color scheme: pink and blue.
When working with only two colors, try 70:30. Between the accent colors in this photo, we can see that in action
We are talking about interior design right now, but these concepts are transferable to buildings, terrain with flora, and organics, among other things.
More examples
Lastly, I’ll talk about biomes.
Besides gameplay mechanics, biomes define the appearance of all enclosed grass, plants, water, fog, and the sky.
Remember, my friends: Swamps are atrocious, and their only redeeming characteristic is the fact that blue orchids appear there!!
End biomes have a dark sky. Jungles and mushroom islands have gorgeous green grass. Soul sand valleys have an eerie blue fog. Nether wastes have a red fog. When you mix the last two in close proximity you get a pink sky. The pale blue water of a warm ocean may evoke different feelings from the rich blue of a deep frozen ocean.
You may or may not notice, but warmer biomes have brighter skies, and colder biomes have slightly purplish skies.
Sky color from left to right: warm, temperate, cold, snowy
If you are at liberty to add a datapack to your gameplay environment, you can recolor your grass, plants, fog, and sky to any color hex you'd like. Bukkit currently lacks a biome API to allow us to create and change custom biomes on the fly, otherwise we'd have plugins to do that already. I'm gonna make extensive use of custom biome colors on my event's map.
I cant wait to see what great things will come from your imagination. Especially collaborations!!