by steps
000000 000000
000000
0000ff 0000ff
0000ff
00007f 00007f
00007f
007f00 007f00
007f00
007f7f 007f7f
007f7f
1111f8 1111f8
1111f8
007fff 007fff
007fff
00ff00 00ff00
00ff00
00ff7f 00ff7f
00ff7f
2222f1 2222f1
2222f1
00ffff 00ffff
00ffff
7f0000 7f0000
7f0000
7f007f 7f007f
7f007f
3333eb 3333eb
3333eb
7f00ff 7f00ff
7f00ff
7f7f00 7f7f00
7f7f00
7f7f7f 7f7f7f
7f7f7f
4444e4 4444e4
4444e4
7f7fff 7f7fff
7f7fff
7fff00 7fff00
7fff00
7fff7f 7fff7f
7fff7f
7fffff 7fffff
7fffff
5555dd 5555dd
5555dd
ff0000 ff0000
ff0000
ff007f ff007f
ff007f
ff00ff ff00ff
ff00ff
6666d7 6666d7
6666d7
ff7f00 ff7f00
ff7f00
ff7f7f ff7f7f
ff7f7f
ff7fff ff7fff
ff7fff
7777d0 7777d0
7777d0
ffff00 ffff00
ffff00
ffff7f ffff7f
ffff7f
ffffff ffffff
ffffff
8988ca 8988ca
8988ca