Why can't I change color scheme inside of blog posts or blog titles on hover?
you can change blog titles color on hover in the main blog settings:
As for the colors in the post page, you can change it is the post page customisation is enabled on your site (we are working to make it available for all users). You can check if you have it by looking for 'Go to post page' at the bottom of the Blog settings 'Main' Tab:
Soon we'll also launch Color Picker allowing to customise the color of single text bits in the blog post.