变色背景

<script>
<!--

function makearray(n) {
    this.length = n;
    for (var i = 1; i <= n; i++)
    this[i] = 0;
    return this;
}
hexa = new makearray(16);
for (var i = 0; i < 10; i++)
hexa[i] = i;
hexa[10] = "a";
hexa[11] = "b";
hexa[12] = "c";
hexa[13] = "d";
hexa[14] = "e";
hexa[15] = "f";

function hex(i) {
    if (i < 0) return "00";
    else if (i > 255) return "ff";
    else return "" + hexa[Math.floor(i / 16)] + hexa[i % 16];
}

function setbgColor(r, g, b) {
    var hr = hex(r);
    var hg = hex(g);
    var hb = hex(b);
    document.bgColor = "#" + hr + hg + hb;
}

function fade(sr, sg, sb, er, eg, eb, step) {
    for (var i = 0; i <= step; i++) {
        setbgColor(Math.floor(sr * ((step - i) / step) + er * (i / step)), Math.floor(sg * ((step - i) / step) + eg * (i / step)), Math.floor(sb * ((step - i) / step) + eb * (i / step)));
    }
}

function fadein() {
    fade(255, 0, 0, 0, 0, 255, 100);
    fade(0, 0, 255, 0, 255, 0, 100);
    fade(0, 255, 0, 0, 0, 0, 100);
}

fadein();
// -->
</script>