I would like to make this cake soon but I am kind of stuck on what they used for the "splatter" on the cake.  Can some of you experts advise me how to go about this???

I suspect it is colored royal icing.

Hi,

I did a cake a few months back with this technique. It is SUPER easy and looks great.  All you need is multiple colors of white chocolate, a bowl and a fondant covered cake.

Do 1 color at a time. So melt 1 color of white chocolate and I used a spoon to sort of drip/splatter the white chocolate onto the cake. It made a mess but nothing a bench scraper can't handle. I held the cake on my hand, tilted, so it was easy to maneuver if I needed and dripped/splattered the chocolate all around the cake.  Once you are done all tiers with 1 color, move onto the next. Once dry, stack and that's it!

Here is the one that I made for my daughters paint party birthday.

http://cakecentral.com/g/i/2912745/a/3297779/i-love-how-this-cake-turned-out-tfl/

Easy Peazy Lemon Squeezy (as my daughter would say)

How pretty!  Thank you SOOOO much!  I didn't know if they had used something special.
 

You are welcome! And good luck.

What type of coloring did you add to the white choc.  Also, do you think the wilton candy melts would work just as well?
 

I just bought the merckens colored chocolates from a local Bulk Barn. I am sure Wilton Candy Melts would do the same thing. I have never used them though.

One thing I found with the candy melts, is that they seem to have a higher sugar content than chocolate so get hotter when melted... I used the to decorate over a chocolate covered cake and they melted my chocolate!! Not sure this would be a problem over fondant but on a chocolate covered cake it might ?

I found with Wilton Candy Melts if I added colour, they would just stiffen the melts...just an FYI
I did a similar cake to this style last year and just used thinned royal icing in squeeze bottles...and although it was quite messy on my table (covered with a new/cheap shower curtain) the end effect was awesome!!  I purchased Americolor Electric gels to use for the colouring.  Good luck! 

I think you can use oil-based candy colors (wilton?) to color candy melts, if they even still make those....I haven't bought them in YEARS!

Yes, you can still get the candy/chocolate coloring that are oil based.  I recently bought some at my local Hobby Lobby.  They have two different sets, four colors in each box.

When melting candy melts in the microwave, it's better to under melt by just a bit, and stir until completely melted, then to over cook them and then they get hard.