Depending on the product, using edible food colours can be pretty straightforward process. But there are quite a few things you should keep in mind when using them.
How to choose a right shade of food colour?
Most food colours have the colour pictured on the packaging, however many factors can cause the colour to vary. So you’d really need to know what you are colouring and how it can react to the colour. A very good example is Swiss meringue buttercream, which is notoriously hard to colour, especially if you are trying to get dark colour. You also have to keep in mind that most food colours deepen with the time but purple will actually turn into blue when left out in daylight.
How to achieve dark colours?
Dark colours such as red, dark purple and black require a lot of food colour. But you have to keep in mind that too much colouring firstly may make the icing bitter. And secondly, food colours will stain your mouth. So whenever you need to get the colours mentioned above for the best results, use gel or paste food colours. You might also consider painting or airbrushing your cakes. One of the hardest colour to achieve, is black. And to make sure you’ll get a true black colour, without using the whole bottle of colour, you might want to start with brown icing first, using chocolate ganache or mixing some cacao powder in your fondant.
What happened to my purple food colour?
It’s not purple anymore, but has turned to blue. This is a very common problem with any purple colour in your cake supply, including fondants, icings and actual food colours themselves. Depending on the colour, if left in daylight, the purple edible colour can turn into blue. To avoid that, keep your finished cakes, fondant, colours and other purple items, in a cool, dark room, or cover them with the box.