When it's time to make colored gumpaste flowers, you can run into complications. Some food colorings tend to fade, which makes the darker colors more difficult to match.
I once made a batch of gumpaste that faded from purple to blue in the space of four hours. I made another one, and the same thing happened. It was another "duh" moment, when I realized that the red food color, which is more volatile, was fading out of the mix, leaving me with blue.
One solution to this problem is to make everything in white, then color the surface of the flowers instead of trying to use a colored paste. You can use an airbrush or dry colors, or both if you're looking for a darker color. Using a colored paste is fine, but you can't be sure that the color will stay the same when it dries.
The best way to get a good color is to do layers, not just one type of color. This gives a depth to the flower, and since real flowers have shades of color in the petals the variation can make them look more realistic.
To make these red roses I started with a dark pink gumpaste and made some quick roses. When they dried, I airbrushed them with red, then used Crystal Colors dusts to add another layer of a deeper red color. By using the colored paste and the airbrush I didn't have to use a ton of the dry color, and I still got a good red that had some depth to it.
As a side note, when I use dry colors I use aluminum trays to put the colors in, so that if I have any left over I can prevent wasting it. I keep a paintbrush for each color in the appropriate tray. Just be careful that you don't dump the tray out by accident, because that stuff will be impossible to clean up. Also hold your breath when you're dusting flowers, you don't want to be sneezing the color for a week after you use it.