No warning to mix screen 0 and screen graphic commands!

[DSMan195276]

if _SETALPHA works on all the image why does not do this work when we omit a range of color to say all colors into the picture?

Well, you never did that You were doing `_SetAlpha 100, 0` which is equivalent to `_SetAlpha 100, _RGBA32(0, 0, 0, 0)`, a specific color value. If you want to set the alpha for every pixel regardless of color I believe you can omit the second argument all together and do `_SetAlpha 100`. Or alternatively with an image, `_SetAlpha 100, , S2`.