I've used a dough hook when I needed a very deep purple and it worked really well. Usually I do it by hand - you just need to keep kneading until it's even. Generally it's streaky for ages then suddenly blends.
Hmm, we're vegetarian so I couldn't do a recipe with marshmallows or gelatin in. Could I use something like [http://www.silverspoon.co.uk/products/decorating/icing-sugars/fondant-icing-sugar this icing sugar]]? Or can anyone recommend a vegetarian sugarpaste recipe?
When I've coloured large amounts myself I've had to get DH to help knead the colour in as I get hand ache! I don't think you could do it in a mixer although I've never tried. You just have to keep kneading and keep kneading... Even colour is just about keeping kneading for longer. Or cheat and pay more for the pre-coloured stuff.
I intend to cover my dd's birthday cake with light purple sugarpaste. The cake is a 11inch by 9 inch rectangle, and according to the calculator on the Wilton website that means I'll need about 48oz (1360g) sugarpaste.
So, I can either buy ready-coloured lilac sugarpaste, which would cost about £16 (!), or buy much cheaper white sugarpaste and colour it myself. (I already have paste colouring which I could use.) Obviously I'd prefer the cheaper option if I could get a good result.
The problem is, I've only ever coloured fairly small quantities of sugarpaste, and even then I've sometimes found it difficult to get the colour even. How easy/difficult would it be to colour a large quantity of sugarpaste and have it remain the right consistency and an even colour? Are there any tips? My electric beaters have a kneading attachment - could that work for kneading in the colour, or would I have to do it manually?