The English use "pants" to denote underpants, whereas the Americans use "underwear" or "underpants."
The word "pants" can be a great source of confusion or embarrassment. In England, "pants" means underwear, whereas in America, pants is used to refer to what the English call "trousers." (In America, "panties" means female underpants, but "pants" always means "trousers," not "underwear.")
E.g., the sentence "I just stained my new pants" has two very different meanings, depending on whether you find yourself in England or America! (Yes, I made this mistake on one occasion in England...)
Colored, in English, simply means that it has been given some color, so a red shirt is colored, for instance. Colorful usually means that there are multiple colors involved, or at least that the object is of some unusually bright, saturated color. My brown trousers, for instance, are clearly colored, as the thread was not naturally that uniform in tone, at least, but they are far from colorful. I am not sure whether this distinction holds in Polish, of course, and kolorowe actually looks to me like it might be the same sort of past participle as adjective as colored.