does anyone know what tip number to use to get this effect of buttercream roses?

do you mean the two-tone color?

if so, it's how the icing is loaded in the bag.

method 1: two colors of icing loaded in bag (easy way -- two small disposable bags each w/ one color and ends sealed shut loaded in large reg. pastry bag that has the tip)

method 2: color striping. using spatula, you take past color and put a big ol' stripe of it down one side of the inside of the pastry bag. Then load in the icing. can even do two or more color stripes and can vary width of strip to adjust effect as well.

I'm thinking you mean the technique more than the color, right? Is there any way you can email the creator?

When you find out can you post how to do it

I'd love to know too. They're very pretty.

ok, to me (and i could be wrong) it looks like two things... 1) one of the methods that Doug mentioned to get the 2 tone look. 2) using any rose tip instead of angling the bag like you to for the wilton rose and making 3, 5 & 7 petal layers, she made longer passes and kept the tip straight up and down (no leaning in or out) and did this with each layer of petals.

at least that's what i'd attempt. if someone knows different let us know..

They look like ribbon roses. You still use a 104 tip but you don't pipe each petal. You hold and squeeze and spin the flower nail till you can't spin it no mo'! then do it again-till the rose is the size you want. I've seen them done in meringue (Martha stewart.com) and royal (Jennifer MI-okay I copied her design). These are clearly buttercream, but I think the concept is pretty much the same.

Here's Wilton's explanation:
http://www.wilton.com/decorating/basic/ribbonroses.cfm

Here's martha's:
http://www.marthastewart.com/portal/site/mslo/menuitem.fc77a0dbc44dd1611e3bf410b5900aa0/?vgnextoid=9affa743fae43110VgnVCM1000003d370a0aRCRD&vgnextfmt=default&rsc=image_1&autonomy_kw=meringue+roses

and here's a pic of Jennifer MI's masterpiece:
http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=852403

that's it alana, what i was trying to describe. i may do these from now on instead of that stupid wilton rose (when i'm not using fondant that is)

Heh! Great minds think alike! I think I was looking for links while you were writing your post because I don't think I saw yours when I started typing mine. They're pretty quick to whip out once you get the hang of it. The person who did the cake in the OP is clearly a master!

I did email the creator and ask her about the rose tip she using.she said she's using 104 but not wilton brand and when i ask her where she got it from,she didnt reply my mail since then .

thanks butterflywing and alana,i will try to do it tonight and hope it will success. the ribbon rose is beautiful too!!will try to practice it tonight also

Not a 104 unless you are making tiny mini roses, you would use the biggest poppa bear 'rose nozzle' aka tube, tip you can find.

Another way to stripe a bag is to pipe a stripe of colored icing down the bag being sure to have the skinny edge of the nozzle in place toward the stripe and then pipe the white into the bag using a big opening. I love to stripe red, green brown and orange icing into a bag then fill it with gold icing to pipe changing leaves. So much fun!