As far as I can tell, there is no law about the colour of the line.
From the guardian.co.uk
Partly because it was so difficult to do business when the law compelled firms to hire by skin colour instead of skill, apartheid South Africa stagnated.
From the economist.com
Bath City's white pants differed in colour from their black shorts and the referee applied the letter of the law strictly, sending several players off the field to change.
From the web.orange.co.uk
I was also struck by how much my parents and my parents-in-law would have had in common despite the obvious difference of the colour of their skin.
From the guardian.co.uk
The Flag law of June 22, 1906 further regulated the use and design of the flag, notably e.g. was a lighter blue colour introduced than was used before.
From the en.wikipedia.org
And if people have those twisted ideas of the world and have those ill feelings toward people who have a different skin colour, I don't think you can say that the law has caused that.
From the economist.com
Federal law recognises a hate crime, and beefs up the penalty accordingly, whenever a victim seems to be picked on because of his race, colour, religion or national origin.