How to chage the color of FONT BACKGROUND when "Opaque" mode is used

Hi,

recently I am moving from datalabel background to font background because it wastes less space, however I am a bit confused on how it works.
I created a wonderful chart and used opaque background for the font of data labels (the background of the datalabel itself is transparent).
the background of the font was set to white, which worked wonderfully

later I updated the colors from another workbook (but without touching the white color) and suddently, instead of white, the background changed to gray -- looking miserable.
Gray has replaced white also in menus such as line weight selection and so on, but I don't know how to fix it --- any help out there?

thank you!!


Bernat

I guess it is an excel mistery...