I like to use calf tail hair for indicators. Some people use yarns but they have a tendency to soak up water and make the fly top heavy, then the fly rides upside down. A sparse bunch of calf tail will not soak up much water. Might try a small piece of bright colored foam.

Cut off a thin bundle of chartreuse calf hair and angle hair butts downward on your side of hook shank. When we make first wrap and tighten, the hair will turn and twist up on shank and it usually turns out okay. It will with practice.
Make a loose wrap of thread around hair wing butts and hook shank.Do not tighten thread until full wrap is made. Some people will make 2 loose wraps before tightening.
With thread bobbin aligned with thread, tighten thread hard pulling bobbin in your direction. Hair will compress and want to twist up on top of hook shank. Keep thread tension tight as we make more thread wraps.
Wrap about 5 or 6 times to anchor. Keep thread tight.
It is tempting to leave it like this, you can see it a mile away. However, the longer it is, the more leverage it has to force the fly to ride upside down.

Trim to just above level of body and head.

Whip finish where you tied in legs and indicator.