PHOTO #4
This is a photo of the L.C. 7020 Ultra-round I use.

PHOTO #5
More detail lines are applied in the same manner as before...only this time using the highlight color.

You can see that the area is acquiring softness and interest and the contrasts are softening, too.

PHOTO #6
Now apply detail lines throughout with the shade color...straight "black" mix.
The contrasts are knocked down even more, & the area has taken on a darker value.
It doesn't look so scary, now, does it? It's starting to look even softer.

PHOTO #7

Before adding the final accent edging, it may be necessary to knock the value contrast down a little more.
(The top half of the photo).

Apply a THIN toning wash of "black". The paint should be the consistency of ink, or a little thinner.
You don't want to lose the light and dark contrasts altogether, just bring everything a bit closer together as well as darken the area a little more.
How many washes vary...sometimes it's just one, others, it may be 3 or 4. Applying them thin gives more control of the build-up of color and value. It's much easier to correct an area that's too light.

Another thing I do often is "spot wash"...applying the toning wash to selected, random areas. This further breaks up a "solid" area of color. It also represents the natural variation of values as they occur in nature. If, after the toning washes, you feel that some tweaking is in order, you can apply additional detail lines of any or all 3 values.

I do this all the time...detail-wash-detail-wash...sometimes as many as 3 or 4 times...using spot washes especially. Just remember to keep those toning washes THIN to maintain some variation of values.
It's a slow process.

Keep in mind that when toning you don't want to bring the value to a very dark color approaching black...the accents of tube black will do that well enough.
Losing your contrasts defeats all the foundation work done earlier.

After you get the overall look that pleases you, it's time to finish with black accents....the darkest value.
This last photo shows the area with the toning washes applied overall. The top half shows the area before accenting...only the bottom half was accented so you can compare.

Sometimes I will mix another toning color into the tube black in order to further harmonize.
Some birds have a bluish, greenish or purplish cast to the black area...many times iridescent (that could be another demo all by itself, so we won't go into that here).
Adding one of these colors to the tube black for accenting contributes to that color bias. I'm using Carbon Black for my accents here, & just for fun, I mixed in a little Phthalo Blue.

There are no additional toning washes over the accenting on the bottom half. This dark value is the sole result of accenting with Carbon Black + phthalo blue.

The accents are applied basically the same way as the other detail lines, except they are concentrated near the edges, and are shorter overall.

Don't paint every barb on the edge of each feather or you'll end up with a hard looking edge. Also, vary the length of the accent lines. Pull some further in near the base of the feather, & end a few about halfway into the feather. If you've inadvertently created a "solid" edge, you can easily correct it by pulling a lighter value detail line through it.

I use this exact same technique with every color I paint.