Hey thanks for the fast response!
I started off with ordering venyl stickers which is rather expensive to 'test' so I feel stuck after ordering a few of them... the next one should be the right one. I'm working on a 50x50cm.
Here you can see the results so far:
Using a transparent sticker:
And a non transparent one:
I tried black 'light' paper between it, I tried white paper, I tried normal white paper, I tried so many things 
nothing works so far...