System Information
Operating system: Windows 10 64bit
Graphics card: NVIDIA GeForce GTX 1060

Blender Version
Broken: 2.80.60, 558017d6a644, master, 2019-05-08
Worked: 2.80.51

Short description of error
When you draw a line in sculpt mode you're unable to see the actual effect if you don't click for each draw the "optimal display" box for the multiresolution modifier.

This is what you have without the "Optimal Display":
Here you can see the dark line...

This is what you have if you turn ON the "Optimal Display":
Here the line is visible..

And now the problem, even if you keep ON the "Optimal Display" trigger, the next line you'll draw will be again a dark light line!!!
Here you can see the line again dark...

Now if I turn the "Optimal Display" OFF I can finally see the line updated.. And for the next line that I draw I will have to do this switch again!!! Every time!

Exact steps for others to reproduce the error
Just follow the step I showed above.

I hope this will help the community.
EDIT: this is my .blend file, try to use the sculpt draw tool on the hair after you use the multiresolution tool:

Kind Regards,
Ernesto