Looking a tutorial to make a custom part!

[Philippe Hurbain]

its possible to make the square 100% transparent (invisible) i want only the sticker visible.
I have tested several colors transparents but i still see the rectangle that helds the sticker

Two solutions (if I understand correctly your configuration, a sticker placed on a rectangular part)
The simple one is to make background of sticker to be color 16 (main color) and use it in the same color as the rectangular part.
The other one is to use special color 0x7000000 which is "invisible".