- OSS project announces logo
- Devs: that's ugly, let me suggest a redesign.
This is obnoxious and disrespectful. Don't do it.
- Devs: that's ugly, let me suggest a redesign.

This touches upon am interesting aspect of OSS: there are different boundaries for different aspects of OSS, and you should respect what the maintainer is willing to entertain.
We often tend to think that OSS = open everything, so even as an outsider we should be entitled to provide unsolicited feedback to any aspect of a project. This mindset is harmful.
Code improvements are mostly objective, but even PRs can be rejected for not providing objective value. Even more so for logo design choices.
Projects often have channels where they are explicitly asking for feedback: RFCs, open design threads, etc. These are good places to provide your feedback!
This is not to say unsolicited feedback should never be made - but please do so like you are offering unsolicited feedback to a real person sitting in front of you. There are things that appropriate and things that are not.
Imagine saying to a coworker "your jacket is ugly and you should be wearing this hoodie instead". Maybe you *do* think her jacket is ugly, but that doesn't mean you should actually suggest that.