color_test.c

#include <stdio.h>
    
/* reference: http://misc.flogisoft.com/bash/tip_colors_and_formatting */
#define GRAY "\e[90m"
#define RED "\e[91m"
#define GREEN "\e[92m"
#define DEFAULT "\e[39m"
    
const int num_colors = 3;
const char *colors[] = {GRAY, RED, GREEN};
    
int print_str(const char *str)
{
	for(int i=0; str[i]!='\0'; i++) {
		printf("%s", colors[i%num_colors]);
		putchar(str[i]);
	}
}

int main(int argc, char *argv[])
{
	print_str("Hello, world\n");
	printf(DEFAULT);
	return 0;
}