How do I change the colour of the showcase image effect. I searched for a way to deactivate it but unfortunately did not find anything.
The image is manipulated in the Twig template file: themes/antimatter/templates/modular/showcase.html.twig and specifically this code:
{% set showcase_image = page.media.images|first.grayscale().contrast(20).brightness(-125).colo rize(-35,81,122) %}
Just remove the manipulations or edit them as you need.
There it is 
thanks for helping here!