I have heard of this trick of using welders glass as a cheap ND filter. But from my childhood experience of arc welding, I was not sure how one would deal with the reality that welders glasses are not really precision optics.
This article addresses at least the issue of coloration and offers some nice tips for adjusting color balance in general.
https://digital-photography-school.com/diy-neutral-density-filter/
Hype Cycles 