Learn Italian: Le matite sono rosse o nere? - Are the pencils red or black?

The singular word is la matita. For regular feminine nouns ending in -a, you make them plural by changing the -a to -e. The feminine word for "the" also changes from the singular la to the plural le, giving us le matite.

Why do the colors rosse and nere end in -e instead of -o or -i?

Adjectives must match the noun they describe. Since matite is feminine and plural, the adjectives must be feminine and plural too. The singular feminine forms are rossa (red) and nera (black). Just like the noun, their -a endings change to -e in the plural.

Doesn't sono mean "I am"?

It does, but it also means "they are"! The verb essere (to be) uses the exact same word, sono, for both the "I" form and the "they" form. Since we are talking about multiple pencils (a "they"), sono translates to "are" here.

Why doesn't the sentence start with the verb, like "Are the pencils..."?

In Italian, you don't have to swap the subject and the verb to ask a question. You can just use the standard statement word order (Le matite sono..., which literally means "The pencils are...") and simply raise the pitch of your voice at the end to show it's a question.