[solved] Change logo in header when scrolling

At the moment I am restyling one of the templates and I have stumbled upon something I am not able to adjust.
My knowledge of css is to basic.

Please go to: overderegenboogbrug.nl/

look at the logo

it is overderegenboogbrug.nl/images/basics/logo_regenboogbrug_wit.png

edit: SOLVED (I decided for a dark navbar)


if you scroll up the static header comes dow, This has a white background
The logo does not work there
I have made a variant with black text.
overderegenboogbrug.nl/images/basics/log...enboogbrug_zwart.png

What to do to make this variant visible?