Colors

All color settings you can find in Theme Settings -> Colors. If you want to adjust background color for all pages, you would go to Theme Settings -> and change default color.
If there are some colors you cannot change it probably means we do not allow, why (?), usually what may seem like a limitation is for the comfort of the user and most likely results from a reason.
You can also change colors for each page in page setting (at the bottom of page editor).
If you really need to make some custom changes, I would suggest using Child Theme. Make sure you buck up before you modify.