I'm not really sure what you are asking. What type of food coloring do you have? You just add a very small amount of color to your icing for pastel colors.
Take a half cup if icing and tint it a light shade of each colour by dipping a toothpick into the gel by 1/4". Then add this to the cup[ and throw the toothpick away. Mix well. Add more white icing until you get the shade you want.
There are NO SUCH THINGS as "pastel" food colours. There is only being able to add such a small amount of gel to icing that you get the right colour. Sorry I can't give you a youtube tutorial because if you can mix icing from a recipe then you can mix the colour in.