I have some off-white or natural or cream colored alpaca (am not sure what color you'd classify it, I found it in a thrift store). Anyhoo, I felted a test swatch of it
, and it felted wonderfully
. In fact, I keep the little test swatch here at my desk and find myself stroking it throughout the day. It seems to relieve stress, kind of like one of those worry stones.
As someone here stated, it's probably the bleach they use to "whiten" yarn which causes it to be unfeltable.