A rainbow text color program

[ChimpFace9000]

Recently there was talk about a program that will create a rainbow effect using html code. So i thought id try making my own. The problem is i keep getting an illegal operation error whenever i run it. I think the problem is in this function....

void GenerateCode(char *String, char *Buffer)
{
	int sLength = strlen(String);	
	int Total = White - Black;
	int IncAmount = Total / sLength;
	int Count = 1;
	int Color = Black;
	while(Count <= sLength)
	{
		strcat(Buffer, "<FONT COLOR=\"");
		strcat(Buffer, (const char*)Color);
		strcat(Buffer, "\">");
		strcat(Buffer, (const char*)String[Count]);
		strcat(Buffer, "</FONT>");
		Color = Color + IncAmount;
		Count++;
	}
	return;
}

If you see a problem in there please let me know, i havent used C++ in a while so i might be forgetting something. Ive also included the full source for those who want to see it.