Architect offices vary for 8 to 80.
There are offices that have dress codes, some have no dress codes.
Some offices will be populated by hipsters. Some offices will be populated by the old muffled adagio of architects all dressed in black. Some offices will allow t-shirts and sandals. I worked with them all.
Check the documentation of the company that hired you. Is there a dress code included?
People who deal with clients - mostly secretarial and architects themselves - wear casual business styled clothes (no ties).
You can check a general "what do Swiss consider business like" here:
Example for Business
Construction managers wear casual clothes: mostly jeans with a collared shirt.
Draughtsmen and Trainees usually wear casual clothes - jeans and a nice blouse/collared shirt. Unless the office is very "young", t-shirts are usually not allowed unless you are one of the 15 year old trainees.
Women's very high heels are usually frowned upon. Needle heels are a big no. Mostly comfortable pumps or flat shoes are required because you never know when you could be called to the construction site. (Please be aware in some offices people actually change into house shoes. This was a cultural shock to me. My current office has a ban on this practice.)
There is nothing wrong with bright colours, but you will stand out because Central Europeans have a taste for the darker or pastel/grey colours. I am easily identified in the construction site because I'm the only one to use bright red. If you are shy and don't like to stand out, avoid them. But you will not be thought less of for using colour.
About jewelry: it's a very individual thing. A big ethnic necklace will work if the clothes are simple enough and the earrings are relatively small. Too busy will be slightly frowned upon.
In the end, depending on the office you will be working, you will notice the dress codes, even the ones that are simply implied, are actually rather lax. Avoid too short skirts, too deep cuts, wear comfortable clothes and you will be fine.