While customizing mods such as Block Outline or Glint Colorizer, when you turn up color opacity to the highest, it goes to vanilla opacity. My suggestion is to allow users to make the colors more opaque like how you can on BLC or other clients like labymod and allow users to type an opacity next to the opacity slider to make it a bit easier for users to set a custom opacity. (no ss sorry taking a break from minecraft for a bit)
#Better color customization when customizing colors in certain mods
fading swan