Help me Improve my fadeIn-fadeOut code

Content
1

default:
red box//visible
blue box//not visible
green box//not visible

when blue button is click//red box fades out; blue box fades in
when green button is click// any visible box fades out and fades in the green box
when red button is click//any visible box fades out and fades in the red box

only one box is visible at a time

the problem with my code is that… it sometimes have a pause when switching from one button to another. can someone c]heck this please… im still noob at AS.

box1._alpha = 0;
box2._alpha = 100;
box3._alpha = 0;
this.bb1.bb1.onRelease = function() {
clearInterval(fadeInterval)
function fadeOut() {
    if ((box2._alpha>0||box3._alpha>0)) {
        box2._alpha -= 2;
        box3._alpha -= 2;
    } else {
        clearInterval(fadeInterval);
        setTimeout(startOut, 0);
    }
}
function fadeIn() {
    if (box1._alpha<100) {
        box1._alpha += 2;
    } else {
        clearInterval(fadeInterval);
    }
}
function startOut() {
    fadeInterval = setInterval(fadeIn, 5);
}

var fadeInterval = setInterval(fadeOut, 5);
}
//=============================================================
this.bb1.bb2.onRelease = function() {
clearInterval(fadeInterval)
function fadeOut() {
    if ((box1._alpha>0||box3._alpha>0)) {
        box1._alpha -= 2;
        box3._alpha -= 2;
    } else {
        clearInterval(fadeInterval);
        setTimeout(startOut, 0);
    }
}
function fadeIn() {
    if (box2._alpha<100) {
        box2._alpha += 2;
    } else {
        clearInterval(fadeInterval);
    }
}
function startOut() {
    fadeInterval = setInterval(fadeIn, 5);
}

var fadeInterval = setInterval(fadeOut, 5);
}
//========================================================
this.bb1.bb3.onRelease = function() {
clearInterval(fadeInterval)
function fadeOut() {
    if ((box1._alpha>0||box2._alpha>0)) {
        box1._alpha -= 2;
        box2._alpha -= 2;
    } else {
        clearInterval(fadeInterval);
        setTimeout(startOut, 0);
    }
}
function fadeIn() {
    if (box3._alpha<100) {
        box3._alpha += 2;
    } else {
        clearInterval(fadeInterval);
    }
}
function startOut() {
    fadeInterval = setInterval(fadeIn, 5);
}

var fadeInterval = setInterval(fadeOut, 5);
}