There are many ways to color leaves…If you want to make some that have veins that are a different color than the leaf itself, you usually have to paint them.
One way to do it quickly is to use wet leaves and apply another color to them before they dry.
To do this you need to have a veiner that gives a good impression on the leaf so that the second color will have a place to travel.
First, take the leaf and dip it into a bath of vodka and food coloring to get the base color.
Put the wet leaf down on a flat surface and take a paintbrush with a tiny bit of the contrasting color on it.
Tap the paintbrush on the center vein on the leaf and let the color run into the first color.
If you want to, you can go back and apply more color, or spread it out a little with a dry paintbrush.
That will give you a good contrast on the veins.