You are most welcome here 
Anyway I already managed to change the color to the whole title, but i’d like to give a different color to each letter (or some letters). So i thought that the possibility to edit it in HTML would be great! I already tried some solutions, suggested i other topics, but they didn’t work.
You can try achieving this by developing custom code to modify widget title. you can refer the code in the custom plugin shared in the following topic to do that.
https://colorlibsupport.com/t/cusomizing-parallax-widget/
Developing custom code for custom functionality is beyond the scope of support that we provide here.
If you are not a developer then you can consider hiring a developer to develop it for you. You can hire a developer from any freelance site. Colorlib recommends the developer https://www.upwork.com/freelancers/~011652ffec8865c6d5