Disable hovering effect thumbnails

[thisisjp]

Hi,

 

I've searched for an answer before coming here and asking for help, but I have not found the solution yet so hopefully one of you guys can help me out. I have the following problem: on the product page the thumbnail of the currently displayed picture is greyed out. Once I hover to the next thumbnail, this thumbnail gets greyed out: 

 

I would like to remove this effect.

Thanks in advance,

JP