#### See: https://music.stackexchange.com/questions/131630/lilypond-opacity-of-objects-slurs-specifically


If you want a dashed slur, use `\slurDashed`:

<pre>
\slurDashed
c''16( b' a' g' a' b') |
</pre>

If you need more control of the dashes you can use `\slurDashPattern` (with a numbers for the dash ratio, and a number for the dash period):

<pre>
\slurDashPattern #0.5 #5
c''16( b' a' g' a' b') |
</pre>

For more options and details about dashed and dotted slurs, see:  
<https://lilypond.org/doc/v2.24/Documentation/notation/expressive-marks-as-curves>

---

To simply change to colour of slurs use `\override Slur.color` (and specify the colour in hexadecimal):

<pre>
\override Slur.color = "#888888"
c''16( b') a'( g') a'( b') |
</pre>