Hello Intensor,
Currently, we do not have transparent background color feature available in the theme but you can achieve it by adding few lines of CSS.
Go to customizer -> Additional CSS and then add following codes.
.page-id-38 .pt-about-cont {
background-color: rgba(191,191,191,.75) !important;
}
.page-id-8 .pt-about-cont {
background-color: rgba(255,255,255,.75) !important;
}
Note: If you change the page then the id will be different so keep in mind to target the exact page ID as your requirement. and also the level of transparency is the last digit in the code “.75”, increase or decrease the value as per needed.
Let me know if that works for you.
Best Regards