Although I cannot confirm your variable declarations for imageBuffer, it should be similar to:
byte** imageBufferPP; /* structure of r,g,b colors */
If it is declared as a double pointer it should work fine.
One other item that you may need to do is to synchronize the (Active) Luxology Environment with the MicroStation rendering settings. Click the RGB icon Drop Down in the lower toolframe and Click the icon "Update Active Environment with Current Background Settings". Do any code related to modifying the luxology settings, then click the Update background settings button, then try to save your image and see if that produces the correct results.
HTH,
Bob