Here is a simple buttercream recipe (double or triple based on how much you need):
1 stick butter (room temperature)
1 lb powdered sugar
1 tsp vanilla flavoring
2-4 Tbsp milk
Cream butter with electric mixer, add powdered sugar and mix, add milk a tablespoon at a time until frosting is the consistency you like. Add vanilla flavoring and whatever you are using to tint your frosting. If you plan to tint your frosting, add less milk so that the addition of your tint doesn't make it too runny. You can use India Tree Natural Food Coloring (buy on amazon here or at Whole Foods), but it is a bit pricey. If you want to do it yourself here are some ideas:
Natural alternatives
to artificial food coloring you can use at home:
Pink/light red –
beet juice from a can of beets (just a little goes a long way!), raspberry or
strawberry preserves, pomegranate juice
Purple – boil red
cabbage & use the juice
Blue – add a little
baking soda to the red cabbage extract or use blueberry preserves/juice
Brown – cocoa powder
Yellow – a tiny bit
of turmeric or Bolthouse Farms Carrot juice
Orange – tiny bit of
turmeric + beet juice or canned pumpkin
Green – cook spinach
until just bright green (don't overcook), puree it and use a tiny bit in frosting