Hydrogen spectrum consists of series of lines. Number of visible lines in Balmer series are 

Though Balmer series corresponds  to visible region only four lines are visible.
$3\to 2\left(\mathrm{Red}\right);4\to 2\left(\mathrm{green}\right);5\to 2\left(\mathrm{Blue}\right);6\to 2\left(\mathrm{violet}\right)$