Vibes
At the end of the day, all I want to see in Solarpunk is the people I love thriving.

Compassion and Healing
I feel at its root that SolarPunk works ought to be compassionate works. Those works can absolutely explore dark topics, but I would want it to be in a healing way. If you want to write torture, grit, darkness... there are so many other genres for you. Go write Late Stage Cyberpunk Witness stories (I sure do). SolarPunk needs to be hopeful at its core.
Anticapitalism, Anticonsumerism
I find it very difficult to envision a Solarpunk future compatible with capitalism. The structures that have brought us to the brink must be dismantled and reorganized in service of a sustainable path forward, and that concept is core to Solarpunk.
Punk and GRIT
I strongly feel that we need to move away from the gleaming, shining skyscrapers with trees hanging off of them and everyone dressed in white. Our modern times and technologies have worked very hard to remove us from the actual work required in staying alive, building and maintaining communities. Any unpleasantness must be glossed over, ignored, or moved to a distance. Solarpunk must be a rejection of that. The work must be SURFACED and made clear. We have to look at, acknowledge and integrate the unpleasant aspects of our lifestyles.
Fashion

For this reason, the concept I'm working on brings in a lot of layering. I'm taking a lot of inspiration from historical fashion, actually, when garments were a lot more expensive. A base of inexpensive lower layers were used and washed far more frequently than the thick, rigid upper layers made of more exotic materials with special detail.
I'm taking secondary inspiration from the modern outdoors community, where base layers are used to help keep you warm OR cool during the day. In present day, base layers aren't cheap! But material science is accelerating rapidly, so I am imagining an interesting material that can be locally fabricated and isn't animal-derived. Dyes at this layer are limited, partially due to additional expense/resource, but mostly due to a desire to limit environmental runoff of dyes or bleach during the frequent washing.
The next layer is a Functional Layer. This one is task-specific, but I do imagine that it will take on a farmer or "blue collar" vibe in general. In the past, we much more commonly saw protective garments like aprons used in the workplace, and I think garments like that will make a broader comeback when everyone will be pitching in for the essentials of community life. This layer is not devoid of fashionable touches, depending on its common use, but the materials chosen are practical and meant to last.
The top Decorative Layer is where things get fun :) I think in a solarpunk future we're going to see a lot more individuality in expression, so it's difficult to pin down what would go into a unified "aesthetic" for a solarpunk world. Like in our current world, your outfit is partially chosen for what you're doing in a day. One key difference is I don't think the concept of "putting together an outfit" will be the same. As I mentioned, the use of dyes and materials is limited in a lot of the layers of clothing, and I think wardrobes will need to be far less extensive overall. Instead of having a lot of different garments, top elements will be used to modify the functional garments underneath them.
These decorative items will commonly be handmade, upcycled, and could travel far and wide through the market network. Intricate decorative arts like embroidery and beadwork make a comeback.
These items are the most expensive and special to a person in this world, so they are well cared for. Decorative mending is a major element of the world I envision:

Sarah Neubert | Fiber Artist (@s.neubert)
(Many cultures throughout the world have a traditional version of decorative mending).
Fast fashion has made its impact, however, and a lot of these clothes are still around. So I also see a future including a lot of weird and interesting "thrift mashup" outfits like we're already starting to see with GenZ:

Jack Sews (@jacksews) • Instagram photos and videos