GIMP 2.10 status of locking icons difficult to see

[Kevin]

It can be done without side-effects:
   

BUT - you will need to copy the theme to your personal Themes folder and re-name it.
Then you will need to edit the gtkrc file in the copied theme to add the following to the end of the file:

Code:

style "highlight-layer-locks" = "gimp-gtkbutton-style"
{
  engine "pixmap"
    {
      image
        {
          function = BOX
          state = ACTIVE
          file = "ui/gimp-button-pressed-lock.png"
          border = { 8, 8, 8, 8 }
          stretch = TRUE
        }
    }
}

widget "*Tree*Button*" style "highlight-layer-locks"

You then need to create a new gimp-button-pressed-lock.png image in the ui folder of your copied theme (copy the gimp-button-pressed.png and modify in a way that suits you)

However, I think you'd be better raising an Issue with the developers: https://gitlab.gnome.org/GNOME/gimp/issues as it is obviously not fit for purpose at present.