Just a colorful square.

Square.go

package main

import (
	"context"
	"fmt"
	"os"
	"os/signal"
	"strings"
	"time"

	"github.com/lucasb-eyer/go-colorful"
)

var rampColorA, _ = colorful.Hex("#5A56E0")
var rampColorB, _ = colorful.Hex("#E0565A") //

func main() {
	fmt.Println()
	fmt.Print("\033[?25l")
	defer func() { fmt.Println("\033[?25h") }()
	defer fmt.Print(resetEscape)

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Kill, os.Interrupt)
	go func() {
		<-c
		cancel()
	}()

	Decode5A3Image(ctx, 16, 16)
	down(30)
}

// Decode5A3Image takes in a 5A3 encoded image and returns an image.Image
func Decode5A3Image(ctx context.Context, height, width int) {
	var pixels = make([][]int, height)
	for i := 0; i < height; i++ {
		pixels[i] = make([]int, width)
	}

	for hb := 0; hb < height; hb += 4 {
		for wb := 0; wb < width; wb += 4 {
			for h := 0; h < 4; h++ {
				for w := 0; w < 4; w++ {
					pixels[hb+h][wb+w] = 1
					printP(pixels)
					if sleepOrExit(ctx, 100*time.Millisecond) {
						return
					}
				}
			}
		}
	}
}

func sleepOrExit(ctx context.Context, d time.Duration) bool {
	select {
	case <-time.After(d):
		return false
	case <-ctx.Done():
		return true
	}
}

func printP(pg [][]int) {
	fmt.Println(black + strings.Repeat("█", len(pg)*2+4))
	for p1, pg1 := range pg {
		fmt.Print(black + "██")
		for p2, pgg := range pg1 {
			fmt.Print(getTermCode(float64(p1+p2)/float64(len(pg)+len(pg1))) + pggToS(pgg))
		}
		fmt.Println(black + "██")
	}
	fmt.Println(strings.Repeat("█", len(pg)*2+4))
	up(len(pg) + 2)
}

func pggToS(i int) string {
	if i == 1 {
		return "██"
	}
	return "  "
}

var black = "\x1b[38;2;0;0;0m"
var resetEscape = "\x1b[0m"

const (
	usefulUp   = "\033[1A"
	usefulDown = "\033[1B"
)

func upC(n int) string   { return fmt.Sprintf("\033[%dA", n) }
func up(n int)           { fmt.Print(upC(n)) }
func downC(n int) string { return fmt.Sprintf("\033[%dB", n) }
func down(n int)         { fmt.Print(downC(n)) }

// getTermCode returns the ANSI escape sequence to set the color based on the given hex code
func getTermCode(percent float64) string {
	hexCode := rampColorA.BlendLuv(rampColorB, percent).Hex()
	var r, g, b int
	if len(hexCode) == 7 {
		fmt.Sscanf(hexCode, "#%2x%2x%2x", &r, &g, &b)
	}

	colorType := 38 // Foreground color

	return fmt.Sprintf("\x1b[%d;2;%d;%d;%dm", colorType, r, g, b)
}