White background showing up as grey? Adobe Illustrator

I have saved an illustrator file using the "save for web" as a JPEG and GIF in CMYK color mode...But a client is saying that the white background is showing up as grey and not white..

The white color value is all 0% :icon_confused::icon_confused:

Any suggestions?
Thank you.
It might be that your colour settings are honouring paper-white rather than true white?
And why does a UK forum flag up colour as being spelled wrongly!?!
You are working in the wrong colour mode. CMYK mode is for print only. Anything that is to be displayed on screen, i.e a website of a presentation should be designed in RGB. Switch to RGB colour mode and use an RGB colour pallet. Your white should be R255 G255 B255 which is the RGB value of white. Dont use CMYK values when working in RGB mode. If this appears grey then your clients monitor is not functioning correctly.