How to deactivate mouse over effect

Hej,
I’d like to deactivate mouse over effect.
I already use this code in quickcss:

.image-overlay .image-overlay-inside::before {
background: none !important;
}

But it disturbs me, that pictures are getting highlited/very bright with mouse over:
http://de.flymotions.com/luftaufnahmen-mit-drohne-naeher-als-nah/

Any ideas what to do? Having kind of arrow change is ok. little zoom in or out also ok. But not having these bright images.

Thanx in advance!
Felix