Light, medium and dark communicate broad roast directions, yet different sellers can use the same label for noticeably different coffees. The source compares these styles through flavour and brewing choices. A colour word is most useful when accompanied by a description of the actual product.
Lighter styles may place more emphasis on the coffee's origin and processing character, while fuller roasting can foreground toasted, cocoa-like or roasty impressions. Neither direction guarantees sweetness, bitterness or quality. Caffeine per serving also cannot be reliably inferred from roast colour alone, because the coffee dose and preparation remain important.
Choose a starting recipe appropriate to the brewer, then adjust according to the result. Record the coffee and water quantities rather than relying only on scoops or a familiar grind number. When comparing roasts, keep serving conditions similar and taste as the cups cool. The practical goal is a style you enjoy, not deciding that one roast category is universally superior.
The conversation
A good question can make a better brew.