I assume you are using v1.0.20190220, if not you may want to upgrade:
  https://github.com/neurolabusc/surf-ice/releases
If you are using the graphical interface, you will want to adjust the "XRay" sliders to change the transparency of the background image and the bleed-through of the nodes. If you are scripting, you can do the same thing with the "shaderxray" function. The attached image is generated with this script:


begin
resetdefaults();
meshload('mni152_2009.mz3');
edgeload('LPBA40.edge');
clipazimuthelevation(0.3, 0, 130);
nodesize(6, true);
edgesize(3,true);
nodehemisphere(-1);
azimuthelevation(250, 35);
edgecolor('actc',true);
nodecolor('blue',true);
nodethresh(1.0,1.0);
edgethresh(0.5,1.0);
shaderxray(0.5, 0.5);
end.