I think the files in the custom folder have permissions like that so they can be editing using the Templates tab in the backoffice. The other skins should work with the permission they have. No need to change them.

Thank you, however I don't know what is their permission in this case skins or plugins because when I downloaded on computer and then upload it on the server they are usually 644 chmod.

However, is it a problem that skin be with 755 chmod?

Is there some security steps with chmoding people have to take after installing b2evo. I read that file permission manual but there is written that you should do that if you have problems after installation.

755 for the custom skin shouldn't be a problem. If you're really concerned, then change the permissions. You may not be able to edit the custom skin through the b2evolution backoffice, however.