Maya has . . . . . . . . blue and . . . . . . . . green pendant.

The indefinite article 'a' or 'an' is used in its original numerical sense of one i.e. to indicate that there is a single unit of something. In the given statement, Maya has two different pendants, one blue and one green, thus indefinite article should be used before both blue and green pendants. If we use it only before blue then the meaning of the sentence will change and it will indicate that Maya has only one pendant which is both blue and green in colour. 'An' can only be used before a word that begins with a vowel sound which is not so in the given sentence. Hence, both blank will be preceded by 'a' article.