Someone

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

int main(int argc, char** argv) {
	if (argc < 8)
		printf("fade <string> <r1> <g1> <b1> <r2> <g2> <b2>\n");
	else {
		int r1 = abs(atoi(argv[2])) % 255, g1 = abs(atoi(argv[3])) % 255, b1 = abs(atoi(argv[4])) % 255;
		int r2 = abs(atoi(argv[5])) % 255, g2 = abs(atoi(argv[6])) % 255, b2 = abs(atoi(argv[7])) % 255;
		int len = strlen(argv[1]);
		float dr = (float)(r2 - r1) / len, dg = (float)(g2 - g1) / len, db = (float)(g2 - g1) / len;
		
		for (int i = 0; i < len; printf("[color=\"#%02X%02X%02X\"]%c[/color]", r1, g1, b1, *(argv[1] + i++)), r1 += dr, g1 += dg, b1 += db);
	}
}