Oh, should explain further.
Mostly OSL is used in a very very dark and dramatic way, so that almost everything else except that which is lit up by the osl is in complete darkness. This is not something you have to do to make this effect, thats all im saying, but if you want still have a lightning from the sun or something plus an OSL you have to tone down the OSL to make it realistic. Something we all know is that a torch doesnt light up as much (well it does it just doesnt show) in daylight as it does during complete darkness. So if you have another light source(daylight, dawn whatever) + OSL the osl will be toned down. This is obviously depending, the thing can be turned against the zenithal lightning making him in shadow and the osl in the shadow which will lead to heavy shadows and heavy lightning whilst the back of the model will have zenithal lightning. And sorry for not seeing the thing you said about coloured glows.. my mistake =)
This technique will be very hard if you are going to do it with a scene that is not in darkness. It will look more dramatic if the rest of the model is like Beelzebrush\'s model (very nice btw, i had not seen it before! that rocket is ace!)