When I started to make this new project, I started with a green button background colour. But during the building proces, I changed this colour into red.

Now my new project is uploaded www.fawltyandjones.nl. On my dekstop and laptop everything looks okay. But on the smartphone sometimes the colour green is shown again. When you use the hamburger menu on the homepage on the smartphone, the colour green pops up again. But when you are on another page, and are using the hamburger menu, then the correct colour (red) shows.

Another example: take a look at the "een heel speciaal nest page, https://www.fawltyandjones.nl/speciaal-nest.html Use the hamburger menu. The background colour is red. Try the same page once again, but scroll a bit down. Then use the hamburger button again. Suddenly there is the green background colour again.

The same happens on every page on the IPhone.

Can you tell me what is going wrong? What can I do to fix this?