Ok, all your LUTs work fine and are very nice indeed.
There must be something wrong in the way i generate LUTs; i'm following cineform.com instructions but i must miss something.
The image shown before was a with a test LUT generated with no effects applyed in it (when i was using curves or a three way the clip was turning blacjk when the LUT was applied)
I'll go back to school and will report here.
Thank you for everything