You can do soap brows with white bar soap.
However clear bar soap works best to do the soap brows but if all you have is white soap bars then that too will work just fine.
I've done soap brows with white Dove Bar Soap and my soap brows turned out just fine.
But when I used clear soap for the soap brows the soap brows turned out much better.
Also when doing soap brows avoid using too much water as the lather can cause your soap brows to look a little white.
To do soap brows you need a Spoolie and a bar of soap.
Simply take a spoolie and pass it over the soap bar and then brush the soap through your eyebrows which should give the eyebrows a nice feathered and pretty texture.