putty background colour change in vi editor

Hello,

I have a problem with my putty session when i use the vi editor or when i do dbaccess on an Informix database.
Suddenly the background and foreground colour of my terminal change and it makes it difficult for me to see whats on the screen.
Why this is happening? Is there a way to keep the same background and foreground colour when i use vi also?
by the way my os is AIX 6.1 if it makes any difference.

Thank you in advance.