Light roasted coffee may range in colour from cinnamon to a light chocolate tan and are more suited to filter styles of brewing where the unique nuances of the bean can shine. Light roasts have prominent acidity as a main component of the extraction, too light and it will taste sour. As you roast darker you are caramelising the sugars more leading to muted acidity notes and more body. Too dark and you are turning the sugars to carbon, which leads to a prominent bitter flavour. A skilled roaster will roast to a profile that lets the coffee characteristics shine in the cup without being unbalanced towards either acidity or bitterness.