[litebox]

Ну примерно вот так:

var color:uint = 0;

var r, g, b, a:uint;

a = 128;
r = 128;
g = 128;
b = 128;

a = a << 24;
r = r << 16;
g = g << 8;

color = color | a;
trace(color);
color = color | r;
trace(color);
color = color | g;
trace(color);
color = color | b;
trace(color);

2147483648 - 0x80000000
2155872256 - 0x80800000
2155905024 - 0x80808000
2155905152 - 0x80808080