An example for using ANSI escape sequences to change foreground and background colours in a terminal.

VT Escape Colours.c

#include <stdio.h>
#include <string.h>

/*
Terminal text foreground and background colours can be changed using ANSI escape codes.
If an escape character followed by a certain sequence is printed to STDOUT, the terminal will change the fore/background colour.

- Foregroud colour sequence: ESC[38;5;{COLOUR}m replace {COLOUR} with one of the numbers from the 8-bit ANSI colour lookup table.

- Background colour sequence: Do the exact same as above but use 48 instead of 38. Making the sequence ESC[48;5;{COLOUR}m

- The ASCII value for ESC is 0x1B or 27 in decimal

- You can also reset colours by printing ESC[0m

More info: https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
*/
void printhelp()
{
    printf("Pass either of the following arguments:\n\n"
           "p - Print the 256 colour palette\n"
           "l - Print 64 lines, each representing four of the colours\n");
}

int main(int argc, char *argv[])
{
    //Literally just overengineering this. You know, *nix style.
    if (argc < 2)
    {
        printhelp();
        return 1;
    }

    //Printing the palette 
    if (strncmp(argv[1], "p", 1) == 0)
    {
        //Padding for the main 16 colours
        printf("    ");

        //Print the main 16 colours, using 48 to select the background colour.
        for (int i = 0; i < 16; i++)
        {
            printf("\x1B[48;5;%dm    ", i);
        }

        //Reset colours and print two empty lines
        printf("\x1B[0m\n\n");
       
        //Print the 8-bit colour palette
        for (int i = 16, j = 0; i < 232; i++)
        {
            printf("\x1B[48;5;%dm  ", i);
            //Print new line after printing new colours
            if (j == 35) 
            {
                j = -1;
                printf("\x1B[0m\n");
            }
            j++;
        }

        //Reset colours and print an empty line
        printf("\x1B[0m\n");

        //Padding for the grayscale palette
        for (int i = 0; i < 12; i++) printf(" ");

        //Print the grayscale palette
        for (int i = 232; i < 256; i++)
        {
            printf("\x1B[48;5;%dm  ", i);
        }
        printf("\x1B[0m\n");

    }
    //Printing colorful lines!
    else if (strncmp(argv[1], "l", 1) == 0)
    {
        //Iterate the colours one by one, print the same text. Using 38 this time to select the foreground colour.
        for (int i = 0, j = 0; i < 256; i+=2)
        {
            printf("\x1B[38;5;%dmColourful", i);
            printf("\x1B[38;5;%dmtext!!   ", i+1);
            if (j++ == 1)
            {
                j = 0;
                printf("\n");
            }        
        }
    }
    //Invalid option, print help and return
    else
    {
        printhelp();
        return 1;
    }

    return 0;
}