Removing highlight from header image

Hi,

I’m currently working on a website for a small company here: http://www.chielcon.co.uk/

I’ve only had the last few weeks to get used to wordpress but I think I finally have the hang of things now. There is one thing that is really bugging me with the site though, if you scroll over the top banner it has some pretty horrible greyed-out highlight appear over the whole thing.

I’ve looked around and can’t seem to find any code or solution that actually removes the grey highlight. Does anyone have any ideas?

I can post my header.php code or css here if need be, just not sure if there’s a line I can put into the css or whether I need to find the code that specifically refers to the header image.

Cheers in advance for any help.