Your making a flower arrangement, but you don't have the right colours, Maybe the pink is too "pink" or the blue isn't blue enough, or you simply cant find the colors you want. You could use fabric dye, but that always seems like too much work for me, and using ink you have more control over where the colours go. Here is a simple way to dye fake cloth flowers using water based calligraphy ink.

Supplies

The flowers you want to dye, (they need to be lighter then the colour that your going to make them, white is best, but pastels work fine as well)
Water Based Calligraphy Ink, (I used Blue, Red, and Black, with a bit of Iridescent)
Gloves

Step 1: Prepping the Flowers

Remove flowers from the stem, most fake flowers have a center remove it as well. Don't lose them

Sometimes the flowers are made out of many layers or have different shapes on the outside/inside, take care not to get the order mixed, it helps to take a photo, or if you have enough, leave one for a reference.

Step 2: Prepping the Ink

Since I want my flowers to be deep blue with a pink/purple center, I'm using 3/4 teaspoon of blue with 1/2 teaspoon water, and 5 drops of black. This was more then enough to dye my two hydrangea heads.

The recipe I used is based on the ink that I have (mine is quite old and a bit thick), different types and ages of inks will have different ratios, so experiment around a bit till you have to colour that you want.

Step 3: Dyeing the Flowers

I wanted my flowers to be a solid colour so I dipped the edge of one petal into the ink and used my gloved fingers to spread the ink throughout the flower.

If you want to dye just the edge or center then use your fingers or a paintbrush to very lightly brush water on the parts you want to dye. Then dab a tiny, tiny amount on the part that you've just moistened, with ink a little goes a long, long way and you can always add more.

Since I wanted my flowers to have a pink/purple center, I added a tiny drop of red to the center, the pink flowers have a darker center that shines through a bit, but it wasn't bold enough so I added red to them as well. Its best to do this when the base coat is still wet so it'll defuse out evenly.