Server Administration :: Installed Database Oracle With Installation

Yesterday i installed oracle 11g r2 by default i installed database Oracle with the installation .but today i tried to create the database with the name green tat also completed successfully..the problem is in startup

export oracle_sid=green
sqlplus '/ as sysdba'
startup
database mounted

select instance_name from v$instance; But it SHowing the instance name as Oracle...i tried with the other method also

export oracle_sid=green
sqlplus /nolog
conn sys/b123 as sysdba

database mounted

select instance_name from V$parameter;

and it shows instance name as green..i tried to see the datafile location for green database

select file_name from dba_data_files; it shows the orcl datafile locations.