Individual post colours – to be same as pages

Hi – I am very happy to donate (how?) if you could help me: I have had difficulties setting up a child theme (it works enough to how the main content page and the logo, but not the pages (menu) or sidebars (custom sidebars). All I really want to do is to set up a child theme and then make whatever amendment is needed in order to get all the posts to use the same colour scheme as the overall site and pages.
Are you able to help me with this and how can I then make a contribution in return?
https://www.beethovenplus.com