NaroCAD had for some time background gradients, yet this made it awful to work with them, because sometimes they were flickering. This is the reason that we patched them using a patch from OpenCascade forum. We also made some ugly yet explicit tricks to make it happen right: we force updating screen after some seconds after NaroCAD starts. The flickering was still there but in rare cases after patching.
I've eventually found another way to do it, flicker free as it seem and also the color theme is a bit more vivid.
The reason is that we display a bitmap based background instead a layers based background which OCC (6.3) seemed to have that much problems with.