I've taken on a wedding cake for June 29.  Since I'll be catering and hosting the reception at my home (30-40 invitees for an outdoor barbecue theme with burgers, polish dogs, root beer baked beans etc etc), we've decided on a rustic buttercream with gum paste fantasy flowers and a narrow fondant ribbon.  It will be a tall cake with at least two dummy layers.  The buttercream will be a blue denim ombre with the flowers to look like they're actual denim (dark on the inside, lighter on the outside).  I'm sure the cake will be no problem to execute and I'm planning to begin the flowers this week or next.  I intend to laminate two layers of gum paste to give the real denim look and I'm using a fabric place mat  as my template to give it the fabric look. 

My problem is how to get the denim color.  I understand that a mix of royal blue with a bit of black will give a good denim color.  Does anyone have a formula for how much of each or am I just going to have to experiment? 

When I have made denim, I like a touch of brown, rather than black. Or a little of each, just depending on what sort of denim you are going for. I absolutely recommend starting with a nice deep blue, and adding a drop of the other color. Since a drop is actually quite a bit, depending on the bottle top, I use the back of a spoon to swipe most of it out, but I rub it on the edge of the bowl, for easy access, if I need to add more. KWIM? I hope that was clear.... Sorry, I am starting to get a migraine, and I am not sure I am making sense!

Also, unless it brand new, stiff dark denim, you can see some white in it. I have done this by spraying it with white flecks, like when the airbrush starts spitting. If you have one with a pressure regulator, you can make it spit by turning down to pressure to about 15 PSI. If you don't have one at all, you can use watered down white coloring, and flick it on the cake with a paintbrush. Test first!

I'm going to have to use Wilton colors as that's what's available around here, and I have to use them up before I order better.  I got the Wilton colors when I didn't know better.  Great idea about keeping the excess on the edge of the bowl for easy access, and I know exactly what you mean (although KWIM had me stumped for a minute).

I also understand what you mean about the white AND the testing first.  I'm hoping the lamination process will do for the white on the gum paste, but the 'flick' method will do nicely for the buttercream.

Thank you for the advice, and I hope you feel better soon.  I woke up with a nasty headache this am myself and its wanting to turn into a full blown migraine.  Was out yesterday helping my daughter buy a car and probably inhaled way too much city fumes. 

Youre welcome, and thank you! I did catch in time. It felt like I was being punched in the head when my 4 year old was laughing (which usually cracks me up!) so I took an Excedrine Migraine. Sorry about the "KWIM? lol

I have to ask, what is the "lamination process?"

Curious to know what the "lamination process" is also.  Please explain.
 

Using denim as an example: The real fabric is blue on the outside and a sort of greyed blue white on the inside.  To get that effect with gum paste for my flowers I will roll out the blue, roll out the white mixed with a bit of the denim color, then layer the two and roll them together.  The result should be a piece of gum paste that is denim blue on one side and the lighter color on the other.  Done correctly, the darker color should bleed through a bit to the lighter side and heighten the fabric effect.

I saw it done on one of the cake challenge shows.  I've done it once with gum paste roses with orange on the inside and a pale yellow on the outside.  Unfortunately they didn't survive to be photographed (lightweight vase, clumsy husband, KWIM, lol).  The hardest part of the process is the rolling it out thinly enough, but I'm supposed to be picking up a pasta roller tomorrow (depending on the roads--we're having a spring storm at the moment and its ugly out there, today will be for the fireplace and a good book).  I plan to use it to laminate the two colors and to impress the fabric pattern onto the gum paste as well. I saw Ron Ben Israel do that with lace to make a mold and it worked really well (for him).  I have a place mat with a well defined fabric look that should do the trick as an impression mat, if not, I'll make one. 

Gad!  I make it sound so easy!  Bet it gives me no end of headache, but I really want this to work.  My bride and groom (DH's brother by choice) are both planning on wearing jeans, and matching the cake to her "dress" is my gift to the two of them just because their families are horrified at the jeans idea.  They're both on their second go-round at the marriage thing, both colon cancer survivors, and because of their surgeries will be wearing something other than jogging pants and hospital johnnies for the first time in a year.  I say with those odds they can bloody wear what they want and hang the rest, but people will get themselves worked up over the stupidest things.  Just the fact that they're both over sixty and found each other is beating the odds as far as I'm concerned.