I am using the free theme of BaseWP, I can only change colors of the menu (also the drop down menu) in the code using a child theme. If I purchase the theme, is it possible to change the colors of the menu and the drop down menu? And is the payment for one time only or annual?
Yes, with premium version you can change menu colors. The payment is valid for a year, after a year you can still use the theme but you must renew your license key (at a discounted price) to have access to theme updates and support.