Note: generalised opinion tutorial, meaning that a minority of people may not agree. This is based off the majority where most people are in (duh)
Tutorial for liveries, not paint tool functions
Also, if you're making a replica, or using built-in liveries this tutorial may not be for you as you are most likely using the liveries from images you see.
Thirdly, this is aimed for starters and/or those who have no taste in art.

Now we begin.

Painting is how we make our planes look good. A good livery would generally make the same build look much better. Here's how to please the most of us:

1. The Basics: Single Color
   Not recommended but is a start. Any color usually will do. Choose a color that fits with your plane's uses.
   Generally any color for civilian planes
   Military camo for military planes, search Wikipedia for details. Usually 2 or more colors

2. Two tone (or more) liveries and designs
   Most planes would usually have 2 or more colors. It is important that your chosen colors:

   • contrast, yet NOT opposites of the color wheel
     OR
   • are similar
     A primary color occupies the majority of the plane.
     A secondary color may be a highlight color, meaning that it is only used on few small sections at a time.
     If you are making realistic replicas/based-off designs, you would have done this.

3. Mechanical part colors
   You might have noticed the colors of mechanical parts

   • on landing gears/engines
   • on wheels
     Instinct tells you what colors they are. (Unless you havent seen a plane/boat/car or even a bicycle):
   • Grey for landing gears/certain engine parts. These are not painted in real life, and the closest you can get to that in SP is grey.
   • Dark grey/black for tires of wheels (unless you are aiming for some fancy tires which are usually not seen in real life)

4. Recommended color assignment on items

   • Main body ("fuselage")
   • primary
   • Nose sections
   • primary or secondary
   • Wings
   • main panel: primary or secondary
   • control surface: similar or different altogether from main wing airfoil
   • Engines
   • most engines have a primary, secondary/highlight and mechanical color (all three classifications I have)
   • the J15, J50, and VTOL engine don't seem to have a mechanical color.
   • thrust ports (VTOL nozzles and RCN) only have 1 color, usually as a primary color
   • fuel tank and inlets (including fuselage inlets)
   • primary and secondary color
   • landing gears, including resizeable wheels
   • 2 mechanical colors, the grey and the dark grey/black used for tires
   • a primary color for retractable landing gear "trapdoors" and supports on wing gears
   • Gizmos
   • shocks, pistons and all rotator types have many colors
   • primary/secondary for airbrakes and/or detachers
   • primary and light color for beacon lights. Note that the "primary" color for manual painting corresponds to the light bulb part.
   • Weapons
   • primary/secondary for wing guns
   • miniguns and missiles have various good color assignments. The main part of these parts should be a primary/secondary color
   • primary/secondary and alternate secondary for rocket pods

5. Others:

   • DON'T use many bright colors (that dont mix) together. Its just awful.
   • using the default built-in liveries is not a noob choice. However, custom liveries give more freedom and may allow for better looking planes.
   • learn from others' (and built-in) liveries! They are a great example of what goes well together. Its the only way to get some first-hand experience.
   • (shameless self-promotion) check out some of mine! ;)
   • as I said earlier (subtly), also learn from real life.
   • pleasing the general population is the main way to go.
   • painting (along with good building and cameraman (yes, seriously) skills) are how you attract people to take a look.
   • please, no clickbait. Youre not Kwebbelkop

Note:
1. General population is the target. In the world we live in, the "different" are hated upon by many. (Though not me)
2. NO flame wars in the comments section. Keep it inside you. Flaming about this topic will only show your bad taste.
3. ^ Flamers will be prosecuted. JK. But seriously. NO flame wars.

Thanks for reading this long block of text
And thanks in advance for no hate comments!