Are you talking about within the nodes themselves or at the main category listing page?
For the category/node itself you can use this in
extra.less
template
Code:
.is-unread .structItem-title {
font-weight:400;
}
and that should (on the default style) use the same weight as the normal read ones do.
For the main category listing
Code:
.node--unread .node-title {
font-weight: 400;
}
should do the same thing.
It will make it hard for your users to figure out what posts are new and what ones aren't easily unless you do something else.