You're conveying meaning with your vocabulary even if you don't mean to. If you don't have the proper words to describe it, that's fine. Like I said, some people even enjoy particular defects in coffee. For instance, growing defects known as 'quakers' have a particular peanuty taste. It's considered undesirable, but some people might like that.

As to your general idea of conveying that light roasts all taste a certain way, I don't think I can agree to that notion. There's such a wide variety of flavors you can cultivate depending on the origin, roasting style, and processing method that you can't really make that generalization.

One thing I will say: many coffees that are advertised as 'light roast', especially in the non-specialty markets, tend to have one or more of the following problems: 1) underroasted (which leads to grassy/green flavors), 2) not actually roasted to 'light' (maybe more medium), 3) poor temperature control, as a result of trying to roast light (leading to 'baked' flavoring), 4) poor coffee selection for a lighter roast, leading to much more green/grassy flavoring as a result.