I am a beginner, and I was wondering why people highlight, with an airbrush, the centres of panels on tanks? Is it because of highlighting or to weather the model and create fading? Personally I dont think its highlighting as you only highlight high points, how is the centre any higher than the edges of panels? If it is fading, then why does fading occur only in the centre, isnt fading random and affects the whole panel?
Please and thankyou

I usually do it to create a little more depth to the model. Also, some times the base color might be a bit dark. So by high lighting or adding a second layer of a lightened base color it prevent the model from becoming to dark with all the weathering. That's just my two cents, but everyone have different approaches and techniques.

I pre-shade and highlight panels so that they seam to have worn differently.

Listen to Mr Yank. He has the right idea.

Thanks guys, Helped me a lot, any more suggestions are welcome

Hi! The whole idea behind fading, highlighting, post-shading, using weathering powders and even dry-brushing is TO FOOL THE EYE into thinking that your subject is out-doors. It's the same technique that film-makers use to create impressions of what isn't really there. All of these techniques enhance depth, detail, shadow effects and bring prominence to raised and added-on detail.

The application of weathering powders and dry-brushing your highlights add to this effect. I stay away from heavy washes and filters because, in my opinion, they detract from the original colors of the model. Careful modulation with an airbrush and weathering powders can convey the effects of dirt, dust, mud, etc quite convincingly without having to resort to the extra time-consuming and messy additional steps of filters and heavy washes. Good Luck!