http://www.faqs.org/docs/htmltut/document/_BODY_TEXT.html
이 방법이 아니라면
마우스 관련 event를 사용하세요.
http://blog.naver.com/naomi007?Redirect=Log&logNo=10001037372

이 아래부분의 스크립트를 페이지 헤드에 넣으시면 됩니다.

<!--여기부터-->
<script language="JavaScript">
<!-- JavaScript
//레인보우 링크 포커스

/************************************************************************/
/* Rainbow Link Version 1.00 (1999.6.10) */
/* */
/* Copyright (C) 1999-2001 TAKANASHI Mizuki */
/* takanasi@hamal.freemail.ne.jp */
/*----------------------------------------------------------------------*/
/* Read it somehow even if my English text is a little wrong! ;-) */
/* */
/* Usage: */
/* Insert '<script src="rainbow.js"></script>' into the BODY section, */
/* right after the BODY tag itself, before anything else. */
/* You don't need to add "onMouseover" and "onMouseout" attributes!! */
/* */
/* If you'd like to add effect to other texts(not link texts), then */
/* add 'onmouseover="doRainbow();"' and 'onmouseout="stopRainbow();"' */
/* to the target tags. */
/* */
/* This Script works with IE4 and above only, but no error occurs on */
/* other browsers. */
/************************************************************************/


////////////////////////////////////////////////////////////////////
// Setting

var rate = 20; // Increase amount(The degree of the transmutation)


////////////////////////////////////////////////////////////////////
// Main routine

var obj; // The object which event occured in
var act = 0; // Flag during the action
var elmH = 0; // Hue
var elmS = 128; // Saturation
var elmV = 255; // Value
var clrOrg; // A color before the change
var TimerID; // Timer ID


if (navigator.appName.indexOf("Microsoft",0) != -1 && parseInt(navigator.appVersion) >= 4) {
Browser = true;
} else {
Browser = false;
}

if (Browser) {
document.onmouseover = doRainbowAnchor;
document.onmouseout = stopRainbowAnchor;
}


//=============================================================================
// doRainbow
// This function begins to change a color.
//=============================================================================
function doRainbow()
{
if (Browser && act != 1) {
act = 1;
obj = event.srcElement;
clrOrg = obj.style.color;
TimerID = setInterval("ChangeColor()",100);
}
}


//=============================================================================
// stopRainbow
// This function stops to change a color.
//=============================================================================
function stopRainbow()
{
if (Browser && act != 0) {
obj.style.color = clrOrg;
clearInterval(TimerID);
act = 0;
}
}


//=============================================================================
// doRainbowAnchor
// This function begins to change a color. (of a anchor, automatically)
//=============================================================================
function doRainbowAnchor()
{
if (Browser && act != 1) {
obj = event.srcElement;

while (obj.tagName != 'A' && obj.tagName != 'BODY') {
obj = obj.parentElement;
if (obj.tagName == 'A' || obj.tagName == 'BODY')
break;
}

if (obj.tagName == 'A' && obj.href != '') {
act = 1;
clrOrg = obj.style.color;
TimerID = setInterval("ChangeColor()",100);
}
}
}


//=============================================================================
// stopRainbowAnchor
// This function stops to change a color. (of a anchor, automatically)
//=============================================================================
function stopRainbowAnchor()
{
if (Browser && act != 0) {
if (obj.tagName == 'A') {
obj.style.color = clrOrg;
clearInterval(TimerID);
act = 0;
}
}
}


//=============================================================================
// Change Color
// This function changes a color actually.
//=============================================================================
function ChangeColor()
{
obj.style.color = makeColor();
}


//=============================================================================
// makeColor
// This function makes rainbow colors.
//=============================================================================
function makeColor()
{
// Don't you think Color Gamut to look like Rainbow?

// HSVtoRGB
if (elmS == 0) {
elmR = elmV; elmG = elmV; elmB = elmV;
}
else {
t1 = elmV;
t2 = (255 - elmS) * elmV / 255;
t3 = elmH % 60;
t3 = (t1 - t2) * t3 / 60;

if (elmH < 60) {
elmR = t1; elmB = t2; elmG = t2 + t3;
}
else if (elmH < 120) {
elmG = t1; elmB = t2; elmR = t1 - t3;
}
else if (elmH < 180) {
elmG = t1; elmR = t2; elmB = t2 + t3;
}
else if (elmH < 240) {
elmB = t1; elmR = t2; elmG = t1 - t3;
}
else if (elmH < 300) {
elmB = t1; elmG = t2; elmR = t2 + t3;
}
else if (elmH < 360) {
elmR = t1; elmG = t2; elmB = t1 - t3;
}
else {
elmR = 0; elmG = 0; elmB = 0;
}
}

elmR = Math.floor(elmR);
elmG = Math.floor(elmG);
elmB = Math.floor(elmB);

clrRGB = '#' + elmR.toString(16) + elmG.toString(16) + elmB.toString(16);

elmH = elmH + rate;
if (elmH >= 360)
elmH = 0;

return clrRGB;
}
// - JavaScript - -->
</script>
<!--여기까지-->