I use this technique on many flies. Even the heads on dry flies get similar treatment. But if I add weight to a bead head I use the thread to colour code the amount of weight.

The way I cover a head is to make the usual whip finish then dub a tiny amount of material on the thread then form a second whip finish with the dubbed thread.

Cheers
Alan.

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"Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, chocolate in one hand, martini in the other, body thoroughly used up, totally worn out and screaming "WOO HOO what a ride!"