文字列のグラデーション      
Sample


ソース
<HTML>
<HEAD>
<SCRIPT LANGUAGE="JavaScript">
<!--
function generate_array(n) {
  this.length = n;
  for (var i = 1; i <= n; i++)
    this[i] = i - 1;

  this[11] = "A";
  this[12] = "B";
  this[13] = "C";
  this[14] = "D";
  this[15] = "E";
  this[16] = "F";
  return this;
}
hx_array = new generate_array(16);
function convert_hex(x) {
  if (x < 17) x = 16;
var high = x / 16;
var s = high+"";
    s = s.substring(0, 2);
    high = parseInt(s, 10);
var left = hx_array[high + 1];
var low = x - high * 16;
  if (low < 1) low = 1;
  s = low + "";
  s = s.substring(0, 2);
  low = parseInt(s, 10);
var right = hx_array[low + 1];
var string = left + "" + right;
  return string;
}
function Rainbow_string(text) {
  text = text.substring(0, text.length);
  color_d1 = 255;
  mul = color_d1 / text.length;
  for(var i = 0; i < text.length; i++) {
    color_d1 = 255*Math.sin(i / (text.length / 3));
    color_h1 = convert_hex(color_d1);
    color_d2 = mul * i;
    color_h2 = convert_hex(color_d2);
    k = text.length;
    j = k - i;
    if (j < 0) j = 0;
    color_d3 = mul * j;
    color_h3 = convert_hex(color_d3);
    document.write("<FONT COLOR=\"#" + color_h3 + color_h1 + color_h2 + 
"\">" + text.substring(i, i + 1) + "</FONT>");
  }
}
//-->
</SCRIPT>
</HEAD>
<BODY>
<center>
<font size=6>
<script>
<!--
Rainbow_string("ようこそ!JavaScript☆Tips です。");
//-->
</script>
</font>
</center>
</BODY>
</HTML>
ワンポイント解説
Rainbow_string("ようこそ!JavaScript☆Tips です。");  の、「 ようこそ!JavaScript☆Tips です。」 を、表示したい文字列に変えてください。