Hello,

1. Do you mean the color of the link at blog post? (https://www.clipular.com/c/5430432090292224.png?k=GTmgt579RnYdTG0hBrlFVHDimi0)
Add this code to your custom CSS box:

.blog-article.standard-style .content a {
    color: #efefef !important;
}

and change the color as you wish.
2. To change the background color of search, add this code to CSS box:

.search_bar {
    background-color: #efefef;
}

3. Please refer to this article for images optimization and for speed increasing of the site. (https://codeless.co/how-i-increased-more-than-70-the-speed-of-my-website/)
Let us know.

Best regards!