Check to make sure that the pins are not damaged. You say that you had purchased an 'adapter.' Might it be a DVI to VGA one? If that is the case, make sure that you didn't bend any of the pins and check if any have fallen loose while connecting the adapter.
Also check and see if the monitor cable itself is bad. You may want to try it in another PC and see if the colors are adjusted.
Of course.. check and see first if any of this could be corrected from the monitor menu... such as tint or something like that.
Hope this helps!