Kool Aid is very easy to get, inexpensive for small amounts of fiber and is available in most groceries in the US.  Dispite what you may think, Kool Aid can give you about any color you want, if you can combine them correctly.  To start you need to do some dye testing to determine what colors you like and also what the plain product actually gives.  The color of the drink pictured on the front is fairly correct, but may be vastly different from the color of the package.

1.  Strawberry Mixade
2. two cherry plus a baby spoon of grape
3. Grape
4. Tropical punch Mixade
5. Cherry over-dyed with grape
6. cherry
7. Slamming Strawberry Kiwi
8. Soaring Strawberry Lemonade
9. Lime green with vinegar from the NEON food colors/sample on right is an apple green dyed in the left overs
   
10. VERY nice dyed in the left overs from 14
11. dyed in the leftovers from 16
12. NEON pink with vinegar
13. NEON blue/vinegar
14. NEON purple/vinegar
15. orange Kool Aid
16. Lemon Lime Mixade
17. Changing cherry kool aid

Final notes, the Lemon Lime Mixade was much nicer than the NEON green dye test. The grape was pretty unattractive, but with some added colors and combinations would be better.

On another note, you can see in the pictures that there are cards that have the dyeing information printed on them. These were purchased Christmas gift tags (the non sticker type). You can make a snip in one side and secure a small sample directly on the card. Store them in a big recloseable bag such as a gallon sized freezer bag, or in a zippered bag that curtains and such items come in. This is a great way to keep track of your results and you will always have them to refer back to.

The extra pieces of wool are wonderful for needle felting, and you can store them all together in a clear plastic bag, and then you have wasted nothing. Consider doing some of your own testing and keep careful records because the one time you don't, will be the best color you will ever get, and never be able to duplicate it.