Hi Petri,
The header in service page is a page hero, the blue background color is added with CSS, you can find below CSS at Customizer > Additional CSS.
.gradient-overlay:after {
content: '';
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
background: linear-gradient(135deg, rgba(24,106,178,0.9) 20%, rgba(0,175,229,0.9) 80%);
}
You can change the color code of background there.
The green/ blue color in page content can be changed in page editor. You just need to edit the page, click on the button or area and then edit its color in block editor.
https://www.screencast.com/t/ksP2jie4D0
Let me know 🙂