Begin with what you can actually see. A useful design note separates an observation from an interpretation, and both from a claim that needs a historical source.
Start with the largest shapes
Describe the main blocks of colour and the shape of the sleeves and neckline. Ask where the eye goes first. Wide stripes, a single panel and an all-over pattern establish very different rhythms.
Then change the distance
Look again at smaller repeats, collar edges, lettering and changes in surface. Which details disappear when you step back? Which remain clear? The relationship between those two views is often more revealing than a list of colours.
Keep the source in the story
A flat photograph cannot tell you everything about texture or fit. Lighting changes the appearance of colour and finish. Record the image or garment you examined, and make uncertainty visible rather than filling it with a confident guess.