When to use white primer?

[ActionButler]

Okay, I need some help with this one.  When is white primer a superior option to grey or black primer?  Admittedly, I have always used a lot of dark/metallic colors on my minis in the past, but, for example, what if I were to paint up some Comstar mechs or some FWL Guards, where I would want the recessed lines and details to be dark?  What would be the advantage of priming white -> washing dark -> painting white opposed to priming black -> drybrushing white -> panel detailing white?

[Rtifs]

You could paint two minis in the same color scheme and you’ll know which one was primed white and which was primed black.  The white primer results in a cleaner, brighter look.  So if you are going for bright colors you’ll want a white primer.  Black is good for darker colors and as a base for metals. 

Of course I do my best painting on organic models, such as 28mm scale.  I’m not so good with machines/mechs.  I just try for an acceptable table top standard.  So for the purpose of mechs, the advice of some others on this forum should supersede mine.

[ActionButler]

No, that gives me a good idea what to expect, thanks. 

I have two lances destined to be FWL & Lyrans that I'll try white primer on.   

[Knallogfall]

It really just depends what look you're going for... Sometimes black is better, other times white, and your techniques make a huge difference as well. For example, I prefer airbrushing over black, unless I use very bright colors like orange or tan. With a brush, you could do white, and use a couple layers of thinned down color for some nice and bright coloration which you otherwise could not achieve with black.

[croaker]

I never use white primer unless I'm planning on a very bright basecoat. I typically use grey, it gives me a nice medium shade.

That said, I've had good results from Ye Olde "Spray-prime white, then do several ink washes" technique on a few things.