黑白渐变

<SCRIPT LANGUAGE="JavaScript">
<!--

function toHex(dec) {
	// create list of hex characters
	var hexCharacters = "0123456789ABCDEF"
// if number is out of range return limit
	if (dec < 0)
		return "00"
	if (dec > 255)
	return "FF"
	// decimal equivalent of first hex character in converted number
	var i = Math.floor(dec / 16)
	// decimal equivalent of second hex character in converted number
	var j = dec % 16
	// return hexadecimal equivalent
	return hexCharacters.charAt(i) + hexCharacters.charAt(j)
}
// set background color to specified descriptors
function setbgColor(red, green, blue) {
	 document.bgColor = "#" + toHex(red) + toHex(green) + toHex(blue)
}
// fade from start to end descriptors (increase step to increase transition speed)
function fade(sred, sgreen, sblue, ered, egreen, eblue, step) {
	// loop to create fade effect
	for(var i = 0; i <= step; ++i) {
		// set current red descriptor
		var red = Math.floor(sred * ((step - i) / step) + ered * (i / step))
		// set current green descriptor
		var green = Math.floor(sgreen * ((step - i) / step) + egreen * (i / step))
		// set current green descriptor
		var blue = Math.floor(sblue * ((step - i) / step) + eblue * (i / step))
		// set background color according to descriptors
		setbgColor(red, green, blue)
	}
}
// -->
</SCRIPT>