If it's only the contours of the white parts (eg. when you use single pixel width lines) then it may have something to do with filtering / mipmapping.
You could try this:
Cleartexturefilters
texturefilter "",1+2
tex=loadtexture("x.png")
cleartexturefilters
texturefilter "",1+8 ; default
But textures without mipmapping may be very slow on some cards. Also make sure your white is really 255,255,255
You could try this:
Cleartexturefilters
texturefilter "",1+2
tex=loadtexture("x.png")
cleartexturefilters
texturefilter "",1+8 ; default
But textures without mipmapping may be very slow on some cards. Also make sure your white is really 255,255,255