Glad you like the theme.
1- I assume you changed the header colour using the Custom CSS? you can apply the same color to the header when scrolling (sticky) by applying the same colour to the class added sticky.
Please give us the URL to your site, and I’ll point you to the exact class you should target.
2- it’s not applicable by default, but I like to believe that anything is possible using Custom CSS and Java Script. If you point me to the URL I’ll help you achieve this 🙂
Please provide us with WP admin access.