To change blog title color in Squarespace, you can follow these.
#1. Determine your Blog Page layout
Edit BLog Page > Edit Section
At Layout, your Blog page layout will be shown
In my example, the Blog page layout is Single Column
#2. Click on the Site Styles icon in the top right of the Header
#3. Choose COLORS
#4. Click on the Theme Color that the Blog Page is using
Follow this post to know what Theme Color a page is using.
In my example, it is LIGHTEST 1
#5. Scroll down to BLOG-SINGLE COLUMN – Post Title , and click on this option
#6. Click Custom then change to the color you want
