You could say 'thank you for the gift it is perfect' or lovely, beautiful, it really is my colour, how thoughtful, unusual, pretty, delicate, useful. These are all positive of course.

You mean nice words, flattering words when the gift is opened in the giver's presence? Or what you say later, after they're gone? Nice words are charming, exquisite, incomparable, magnificent, pleasing, smashing, spectacular, tasteful, stunning, superb, splendid, or wonderful.

cool, nice, great.