i have been giving a cake order which must look like this. this is my very first wedding cake order. I do not have a problem with fondant bit but i am afraid if i use royal icing to make the lase and the strings the black colour might bleed on my cream fondant.  please help me out the wedding is in a few weeks.

I've piped black royal on white fondant with no bleeding...I hope someone else shares their experience.  I can't remember if I refrigerated it but I want to say I did because I think it had cannoli filling in it. Why don't you do a test run. on a small cake- maybe that will put your mind at ease. 

Yes, you can pipe black RI onto light fondant without it bleeding. I recommend waiting until the fondant has dried on the surface - so cover one day and pipe the next. Do not leave any corn starch on the surface. Also, test both YOUR fondant and YOUR RI, because what you use may be very different to me or the next person.

IF you have never piped black RI onto light fondant, though, maybe your first wedding cake is not the ideal time to start? 

The issue is, if you make a mistake, you cannot remove ALL traces of the black RI from the light fondant. So you need to be very competent and very careful. 

I have also done similar piping using melted dark chocolate...that again presents a bunch of difficulties.

Good luck with it :-)  Make sure you post a photo of your cake when its done!