Hi Partner,
You can easily change background color of the all page through editing HTML.
--Under 'HTML' tab, find body style, add it: background-color: rgb(232, 232, 232);
Please refer to the following for more details:
1.When you add one form to the marketing page, the form element is put in the column, and column is in the section,outside of section is the rest of the page.
2.The background color of the column will impact form, you need keep it white.
3.To make it easier for you to tell the difference, I've set another background color for section(Just for testing):
--For the section color in your example, you can choose either white or light gray, both of which are fine.
4.Under 'HTML' tab, find body style, add it: background-color: rgb(232, 232, 232);
5.Result:
Note: color converter
I hope you can mark my answer verified if it is helpful! If you have any questions, please feel free to contact me.
Regards,
Leah