Adjust color in photo of an auditorium screen during a presentation

[RobertBU]

I have many photos taken during various presentations in an auditorium. Although the screen looked white to the people in the audience, the screen looks blue in the photos. Is there some way to correct this, while still keeping the colors that were in the slides that appear on the screen? For example, if the image projected on the screen has text in blue, I don't want to lose the text color in the process of correcting the screen color. 

[edgrimley]

The image that you posted is on an angle so the blue backround isn't uniform and gets lighter on the right side. Set the blue color as the forground color, add a solid color adjustment layer with the blue color and set the blending mode to divide. That should turn the blue into white. I selected the blue color on the right side so only that area is white.

[c.pfaffenbichler]

That image seems to have problems (with noise for example), do you still have the RAW file? 

It might be easier to do the correction in Lab.