Can some one help me please. i need to make this cake for my nephew, can you tell me how i can make this background, the blueish parts. i dont have an air brush so thats out, any other tips most welcome. i will be doing it in butter cream (only butter not shortening) is it powder colour, gel, etc

http://www.flickr.com/groups/945826@N25/discuss/72157623384337619/
(Mod edited to provide working link.)

This is the pic that i am talking about. Thank you.

I also don't have an airbrush, so I would knead together fondant in different shades of blue and not completely mix it. The effect will not be exactly the same, but you could get it close.

If you are using a crusting buttercream then you could dust it with a soft brush and petal dust. Otherwise perhaps you could fill a couple of bags with the darker shades and swirl them through as you cover the cake with White.

That seems more complicated on paper than in my head so I've probably been as clear as mud. Hope it helps anyway.

Yours aye
Puss

I just realized that you asked about buttercream...NOT fondant...Sorry...I think I'm going to need a second cup of coffee to get this morning going

Thank you all for your tips, more welcome. i wish i new the person who made this cake and asked them. shall give the petal dust a try or even light blue luster dust a try.Tried the swirls of light blue butter cream, mmm ok, but still doesnt look like the picture. thank you once again for your prompt response

You might be able to use the spray on colors by Wilton. I have never used them but they seem to be the closest thing to an airbrush I can think of...HTH
You can buy them at Michael's but I put the amazon link below just so you would know what product I was referring to. It comes in a variety of colors.

http://www.amazon.com/dp/B0000VZPIQ/?tag=cakecentral-20

The blue spray on, i was told was a bit too dark for the pic. that was my first choice. thanks anyway. i have never used them. wonder if any one else has used it and got a very fine, light spray.

Just a suggestion, but if you cant find the supplies to do the airbrush technique, you could always just ice the background in solid blue and pipe on some textured clouds. That is a cute cake.. my 2 year old LOVES In the Night Garden! Good luck!