I usually colour my milk/cream before adding to my white chocolate. The only drawback to that is you don’t know how much gel colour to add to achieve a specific colour. So I do a base colour, then use a oil based chocolate colouring like colour mill, roxy & rich or wilton candy colour etc. added to the ganache afterwards to achieve the colour I want.
-- Creativity is God's gift to us. Using our creativity is our gift back to God. Clarky's Cakes 😎
If you want to airbrush, SugarPrism.com carries Edible Oil Paints and Edible Acrylics that can be airbrushed over ganache. They are opaque so coverage is a dream. Michelle also has some free videos about this and is great at answering Qs.
Like June, if I want to color my ganache, I add the gel color to the cream before pouring it over the chocolate. It is really hard to gauge how much color is required, so use sparingly. If you want a specific color, it would probably be easier to dry brush it with petal dust, once the drip has completely set.
Another option is to use candy melts in the desired color. I’ve used candy melts and several different types of white chocolate (chips and bars) for ganache and I don’t find a great deal of difference in taste, when doing a drip. It is such a thin layer of chocolate, it does not add significant flavor, so the type of chocolate matters little. That is my opinion, of course. Some bakers are probably horrified that I even suggested candy melts.
-- Sugar Sugar by SSmiley
I normally add my color to the panache just like June and Sandra💖if you do an airbrush style would love to see how it is done 💖😊😍Hope it turns out awesome 💖😊
-- Dubey Cakes