I think you’re facing two issues which are interrelated.
First I would replace the PRAM battery which is located on the bottom right side of the logic board. Follow this guide to Step 12 [guide|8968]
[image|1688159]
Once replaced lets reset the display
* Start by choosing Apple menu > System Preferences …
* Select the Displays Preference Pane
* Click the Color tab
[image|1688161]
As soon as you do the washed out screen should be gone.