separator block default color change

Hi, I'm trying to change the default color of seperator blocks.

Seperator blocks are the blocks that add a little line -------------- like this as a paragraph.

On my site, their default color is grey and I can change them manually to white, but I rather the default color be white and then I can mannually change them to grey.

Any help would be greatly appreciated :)

I added a link to the post that has a few of these seperators..

Thanks again for everything,
C