Rules of Ultimate
3. Equipment
3.1. Any flying disc acceptable to both captains may be used. 3.2. WFDF may maintain a list of approved discs recommended for use. 3.3. Each player must wear a uniform that distinguishes their team. 3.4. No player may wear items of clothing or equipment that reasonably could harm the wearer or other players, or impede an opponent's ability to play. Annotation: Harmful equipment should not be worn
This could include, for example, wristwatches, bracelets, buckles and protruding jewellery. Fully metallic studs, long studs and studs with sharp edges are not allowed on footwear.
Steinar's comment (unofficial!): Covered watches
Many players want to track their workouts using a watch; if using a soft armband over it, it should not be dangerous even if one inadvertently hits another player in the face and as such seems to be allowed. I've never seen someone object to it.
Annotation: Equipment that impedes ability to play
This includes oversized items, long pieces of fabric etc. The types of gloves commonly worn by Ultimate players are allowed, but they must not in any way damage the disc or leave any residue on the disc.
Steinar's comment (unofficial!): Standard discs
In practice, the standard disc worldwide is the 175g Discraft Ultra-Star. EUF events use Eurodisc, which is pretty similar. It is very common for game discs to have white as the main color.