Yes !
It's possible via minitweaker
http://www.subsim.com/radioroom/show...&postcount=725
Download this mod, and set the values yourself to have a blue light at daytime.
ps : you can change the colours for night and day separately, and you can even change the colour of the light for CR (command room), RR (radio room) and CN (conning tower) separately. :p
There is no trigger to have a blue light when silent running though
... It's a hardcoded thing, unfortunately.