Support how to change color of locked screen pin pad

Hi I'm new here, my first post. I've been fiddling about with settings quite a bit today, trying to optimise battery. I'm impressed with how much the settings allow customisation of practically everything.
Anyway I've always elected to have a pin as my unlock security. I haven't change that. However after all the playing I did with settings I've managed to change the color of this pin pad on the locked screen from a lovely blue which appeared to be the default to a boring gray color. The whole screen is gray - black & white - when the screen is locked.

I have can't find how to get it back.

Any ideas anyone?

Thanks