Answer: "I tried several new foods on my trip: sushi, dragon fruit, and lychees." and "Diego studies three kinds of dance: jazz, modern, and tap."
Explanation: In the first and last sentences, there shouldn't be a colon (or any punctuation for that matter) between the verb (call/buy) and the direct object that verb takes (her grandmother, etc./seeds, etc.). In the third sentence, the colon should be placed after <em>collage</em> (it is not an item of the list that follows) and a comma should replace the colon before <em>and.</em>
The answer to your question would be that the sentences that are correctly punctuated are the following ones:
I tried several new foods on my trip: sushi, dragon fruit, and lychees.
Diego studies three kinds of dance: jazz, modern, and tap
Explanation:
A colon means "that is to say" or "here's what I mean". In both cases, we can see the use of the colon to introduce an item or a series of items. You should never capitalize the first item after the colon. In the first example, it introduces the new foods tried by the speaker and, in the second case, the three kinds of dance Diego studies.
