Parallax background opacity

Hi

I have been trying to figure out how to get the opacity or overlay correct when using the parallax option.

Now the 2 images seem like being overlaid with a black (transparant) layer. It takes away the vibrance of the original images.

Where can I fix this? Have tried adding

.newsletter,
.contact-us,
.packages,
.header {
    background: none repeat scroll 0% 0% rgba(0, 0, 0, 0) !important;
}

but this only affects the ‘real’ (overall) background (standard is the city+yellow cab), not the parallax backgrounds.

Thanks

EDIT: added image for explanatory reasons:
https://dl.dropboxusercontent.com/u/18798185/Schermafbeelding%202016-01-23%20om%2018.53.17.jpg