Hi, every time I make my buttercream to ice my cupcakes the colouring will not blend properly. The colour always appears with the 'butter' showing through. I'm using Wilton icing colouring paste. Yellow appears to blend fine, but rose pink or royal blue always appear streaky. Every time I've tried this I get the same results, I try blending it more/less but to no avail. Any tips would be handy. Thank you.
Usually food colour pastes are very good for tinting buttercream as they are concentrated so you only need to use small quantities. It is best to add the colour a little at a time, using a clean cocktail stick (toothpick) to add the colour to the buttercream. Beat well between each addition to distribute the colour and add a little more if needed to get your desired tone. Make sure that your buttercream is at room temperature so that the colour blends easily.
It is also worth bearing in mind that buttercreams made with all butter will have a very yellow base and this will affect the final colour of the buttercream. It can be difficult to get a "true" colour. If you want a proper pink or blue colour you may need to make a buttercream with some/all vegetable shortening to get a suitable pale base (a meringue based buttercream may be a good option) or you could use a store bought white buttercream.
Coloured buttercream will also sometimes darken slightly while it stands so if possible tint it 2 hours before you use it to make sure you have the correct colour. If it is streaky you may find that beating it after standing will properly distribute the colour.
The gel pastes can dry out if they are not used that often and this will make them more difficult to blend (the paste becomes sticky and thick). Make sure that the container is tightly sealed after use and you may find it useful to put the container in an airtight box or seal tightly in a plastic bag. Store the colours in a cool, dry place away from direct light.