Hmm, not exactly. In this case i thinkthere's no declination. Du bist rot. If you use, Die rote Jacke (with preceding article - weak declension), or Roter Apfel (without - string declension) http://en.wikipedia.org/wiki/German_declension#Attributive_adjectives someone correct me if i'm wrong please.
But these lessons with adjectives should have introductory grammar. Dissappointing that there isn't.
sorry but i strongly disagree. in this case, it's so diverse that it gets too complex to learn without rules and just trying to figure out and detect the paterns from exemples. look, there's 3 scenarios: 1) Not preceded by article -> Strong 2) Preceded by definite article -> weak 3) Preceded by indefinite article or possessive pronoum -> mixed.
then, for each of the three scenarios you have to take into consideration 3 genders (plus plural) and 4 cases! I say it's a very complicated matrix to try to figure out for yourself.
In the first lessons, like dative acusative etc there was an introductory grammar explanation and it was much more simple, so why not now?