Vivid random colors

If you want more control over how to create random colors, you need to steer away from the RGB space and go into the more human-friendly HSB color space, which is Hue/Saturation/Brightness.

Unfortunately flash doesn't natively support this but you can convert between the color spaces using some help functions like the following which were found here:

function hsv2rgb(hue, sat, val) {
var red, grn, blu, i, f, p, q, t;
hue%=360;
if(val==0) {return({r:0, g:0, v:0});}
sat/=100;
val/=100;
hue/=60;
i = Math.floor(hue);
f = hue-i;
p = val*(1-sat);
q = val*(1-(sat*f));
t = val*(1-(sat*(1-f)));
if (i==0) {red=val; grn=t; blu=p;}
else if (i==1) {red=q; grn=val; blu=p;}
else if (i==2) {red=p; grn=val; blu=t;}
else if (i==3) {red=p; grn=q; blu=val;}
else if (i==4) {red=t; grn=p; blu=val;}
else if (i==5) {red=val; grn=p; blu=q;}
red = Math.floor(red*255);
grn = Math.floor(grn*255);
blu = Math.floor(blu*255);
return ({r:red, g:grn, b:blu});
}
//
function rgb2hsv(red, grn, blu) {
var x, val, f, i, hue, sat, val;
red/=255;
grn/=255;
blu/=255;
x = Math.min(Math.min(red, grn), blu);
val = Math.max(Math.max(red, grn), blu);
if (x==val){
return({h:undefined, s:0, v:val*100});
}
f = (red == x) ? grn-blu : ((grn == x) ? blu-red : red-grn);
i = (red == x) ? 3 : ((grn == x) ? 5 : 1);
hue = Math.floor((i-f/(val-x))*60)%360;
sat = Math.floor(((val-x)/val)*100);
val = Math.floor(val*100);
return({h:hue, s:sat, v:val});
}

So to create vivid random colors you just randomize the Hue, and set a high Saturation and Brightness. If you just want random shades of a color, you set the Hue and Saturation and just randomize the Brightness.