I use some code:

$colors = array ();
$colors['test'] = imagecolorallocate($img, 0 ,1 ,2);
....

It works until I change picture to other
After that imagecolorallocate and imagecolorallocatealpha return false
$img is correct image, i.e imagepng print it correctly

How to make imagecolorallocate work?

Comment on the documentation of this function:

If you even in a situation where it's not allocating the color you want it could be because of your images color allocation table. GIF and 8-bit PNG images are very susceptible to this.

If your using an GIF and PNG try dropping a color from the table, should let you allocate another.

If the source image in an indexed image (8-bit or less) then make sure there is room for additional colors. E.g. an 8-bit image might not be using all 256 colors from the palette in that case the function should succeed and it will not otherwise.

Edit

I looked at your image and it is infact an 8-bit PNG image that uses all 256 colors. Try converting it to a true color image (either via photoshop or by copying the image into a GD image created via imagecreatetruecolor()); do all the editing, then save as GIF.