If it's moist it's one of the oils such as lanolin, or suint.
Sometimes there are yellowy or white flakes of dry dandruffy stuff - skin flakes.
Lanolin washes out in hot water, the dandruff is a nuisance and more difficult to remove. It will come out during processing, but many folk don't like it. If it's for you, then turn the fleece cut side up and go over it with shears to cut off the flakey stuff at the bottom of the staples.
If it's stuck to the hairs it could be nits, or mites are I think orangey and seethe around near the skin.
As always, not possible to be accurate without seeing it. Have a look with a strong magnifier.