"Mark all as read" link is not visible

[emptyset]

but the thing should be completely removed(or commented out) or readded

Does it cause so significant performance and/or usability issues that its removal is considered?

It's intended to be less visible

Why hide it? If there is harm from it being common knowledge and available to everyone, why not remove it or restrict (or throttle) access? If there are no such negative effects, any and all positive effects are your reasons not to reduce visibility.

If we discard the requirement to conceal the link, even #009900 would be a noticeable improvement (currently it's "green" or #007F00). #00CC00 is even more functional.