Okay, I understand how to marble fondant. What I don’t know is how to get the effect of it peeking out on a solid colored cake. Any tips? 

That is a separate piece inserted into the surface., so, I would guess, cover your tiers in the solid, cut out the shape/size/section where you want to insert the marble, lay the marble piece over and cut to fit? Looks like the gold leaf disguises the seam.

Oh, I forgot, after covering in the solid, assemble the tiers, then cut out the section that is to be marbled.. unless someone has another suggestion.

Agree with gscout73.

This is beautiful but I’m amazed by how many black cakes are being made these days.   I would hesitate to eat it 

I actually like this look more than the geode cake. But that is just me.

So do I, gscout73, or at least as much.  It is stunning.

kakeladi, I don't think black fondant is as bad for staining as buttercream and I know a lot of people will do a chocolate frosting and finish bringing it to black with an airbrush.  I have not tried that yet, but it is on the list.

gscout73 information is exactly how I am sure this effect was achieved. And why kakeladi would you be hesitant to eat? You could peel off the fondant anyway. I love a all black cake too Sandra. They are very striking, especially with a pop of colour added somewhere.

Beautiful to behold but the thought of eating * black* turns my tummy:)  I’m not  a huge fan of cake I go for the icing! To peel off the fondant defeats the reason for having a slice :) 

I've had already tinted black and the amount you are getting on a slice of cake, per bite, really is not that much. Speaking for myself I have not had a problem with black. The example cake shown is beautiful with the dark blue. I can imagine using a rich chocolate brown with marbling.

gscout73, I think the dark chocolate would be just as attractive as this one, without the food coloring.

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Oh, yes, definitely!

Kakeladi, I see no reason why this couldn't be done with buttercream or ganache with just the marbled portion being done in fondant.  Just do it in reverse of the all fondant method mentioned.  Completely finish the tiers in the solid color, let them set up well, apply the marbled fondant and highlight with gold.  I really, really want to make one of these.