Yes you must edit the line that refers to color and give it the hex-reference for blue in all entries for the mask. Sadly I don't know which one that is, but the entries in the menu.ini file are in attack and observation scope right after the redlight entry (Which is I11). You must change I12 to I19 colours, in this line:
[G26 I12]
Name=BottomRight
Type=1030;Static bmp
ItemID=0x26120005
ParentID=0x26120000
Pos=365,-342,295,295
Color=0x96000050
Materials=1
Display=2;Linear
Mat 0=data/menu/gui/redmask.tga
Crop 0=1,1,-1,-1
MatFlags=0x9
TexFmt=0x29
The number in this example is red, but changing it you can get any colour, I have made it green to allow my new reticle to be visible in the dark as the original one does