Flat color section

Hi designers,
I'd like to post a question that I've been wondering, it's about the flat color section in the DC canvas, I believe it's suppose to be used for a version of the design with flat colors, which mean without gradation, blur, and other effects, is it right?
I've been observing several designs that seemed to be using the section for inverted version, or to show how the design would be when put on dark background. Is this allowed?
I experienced that sometime the CH asked designers to present dark background version, but up to now I'm avoiding using the flat color section to do so.
If it's not allowed, would it be nice if the canvas has a section to do that?

I'm sorry if it's already posted before, but I couldn't find it in the forum.

You can use a back for reverse in the flat color area only unless the CH has requested a background then you can use the main area with a background

Is it allowed to use Gradient in Flat color portion? I don't think it is, but I just saw some designer do, And i just wanna make sure. Also is it allowed to put a reflection smoky shadow under the flat and B/W portion? Just to popup the B/W and the flat a lil bit.
Kindly advise.

Thanks,
-Amr

if the shadow is part of the logo. You can use a flat background in the flat section.

Thanks Sharie, so the flat color area can be used for that purpose, how about the gradient asked by GoldenZ ? because I think it is not allowed even if the shadow is part of the design, so it has to be a flat shadow.
For the B/W area, I'm pretty sure that no smoky shadow should be applied, since it can't contain shades of gray. Please correct me if I'm wrong

Ok so are there actually design guidelines for the Flat area? I am new to this and am curious as to what is truly meant by "Flat". If this has been posted somewhere already then please post a link so that I can go read the posts.