Birth control question? when should i get my period?

so my last period was the 31st, i started birth control pills on the tenth of june, and i was supposed to get my period the 21st. However, the 21st doesn't fall on the "designated period pill days" (you know how there are a different color pill for the days you're supposed to have your period) so when should i expect to get it? will it not come till i've reached the colored pills? is my body just getting used to the hormones?