>>88298
By grid hatching I mean the more extreme form of dithering on the Sand Elemental arms and Cloud Elemental breasts where the patterns are very clear 'X' or 'O' shapes supported separate with lanes of a 'grid'. The single alternating pixel dithering on places like the Cloud Elemental's sports bra blend in perfectly at the fairly large resolution.
Notice that on your two pics here, neither dithers the main character. The Saya pic dithers the background, and that's generally the historic use case: it drew more focus to the sharper character while at the same time saving on background colors used when the older systems this originated on usually had a limit of 16 or 32 colors.
Which leads us to capturing that classic vibe. There are really 4 parts to this so I'll start with the most immediately useful one: to teach yourself, start with a 4-color ramp of shadow > darker midtone > lighter midtone > highlight. You have a scale of 0-255. Cut off the bottom 30 or so as all pretty much black. Now ramp roughly +40 for each step. On a bright character you might start with the highlight and go 250 > 200 > 160 > 120, while on a darker character like my Hellhound above you'd start dark and go 40 > 80 > 120 > 168 > 216, the last being for the rare very bright spots.
But we have three colors. What about the other two? The second lesson is about color shifting, which is fairly general. The idea is to let you ramp into multiple adjacent colors, like I do above with my Myconia. The two colors are whitish-pink and purple, and since purple is naturally darker I chose the shadow to overlap. So I start upping the blue relative to the red, which is strongest. From bright to dark, the RGB colors are [248,240,216], [248,176,192], [200,128,160], and [144,88,136]. This naturally ramps into the purple mid-dark tone of [96,64,120].
This second rule is quite a bit more flexible depending on what you want to do. The vaporwave/cyberpunk color scheme will use bright cyan as a shade on neon pink, because blue is a naturally "cooler" color, and is enough different that it stands out even if value-wise it isn't so far apart. Meanwhile, if you want an "ancient" vibe like your cloaked statue, presumably made of bronze, you add a little green to everything, which at darker tones gives the "graying" effect, but even on the highlights causes desaturation, the highlights being intentionally lower to fit the mood. So neon pink is [255,0,255] vs. cyan [0,255,255], making that brand of cyberpunk an intentional eyeburner, while on the statue even the brightest "coppery red" is [144,138,111], only halfway up the scale and creating a dark, muted ambiance.
That's the third part, no longer even a rule but a question: what mood do you want, and why?
Let's say that you decide on a fantasy setting where the hero will enter the Monster Lord's castle under the moonlight. Do you want to play up the romanticism and compliment her visage as an ethereally beatufil Lilim, or lean into suspense so that it's not even obvious this is a guy-meets-monstergirl situation for as long as possible? That chosen, are there other goals? If it's a playable game area, you probably want somewhat less palette unity, so the playable areas are obvious and are darker than the characters. So I'm including three examples, from Seiken Densetsu 3 and Castlevania X on the SNES, and Super Cauldron on the Amiga. Cauldron plays up the brightness, good for romance, Castlevania leans dark except the full moon because c'mon, it's Dracula, and SD3 hits a middle ground. All stick roughly to the 4-color ramps.
But I think you're more interested in characters, and I chose the scenes more because it's much harder to find 3 pixel renditions of one character with such different takes on a similar scenario. So for the final part let's look at 90s Japanese Cyberpunk, before the vaporwave color scheme came in vogue. I don't even have the game title anymore, but this is art you can aspire to, and on a mere 16 colors!
The lesson is how to break up the tones, a fundamental skill for pixel and anime/cel artists.
We have a 4-ramp blue gray and a 5-ramp skin tone, but rather than dither, the artist makes the bold choice to switch at just the right moment. So for her breats, we get one shade tone except a little where boobs meet dress in the middle, a little at the point of deepest cleavage above that, and a bit below her nose and lips because her left (our right) is shaded more. This skill is learned by observation and practice, and while I can give some tips, ultimately you must learn to see the forms yourself. Master it and you not only master an oldschool vibe, you become a superior artist full stop.