What is the format background-color:RGB(var(--now-color_alert--positive-50, 50, 205, 50));?

[Rain Vaine]

Hello, 
I am trying something in field style and encountered this structure:
background-color:RGB(var(--now-color_alert--positive-2, 37, 131, 43));

It seems that it just works by inserting the color rgb to the value, for example:

background-color:RGB(var(--now-color_alert--positive-50, 50, 205, 50));
I just repeat the first value to get the four value set. 
My question is what is this part really "--now-color_alert--positive-50" and am I doing it right?

And about the other format for field styles. what is the ideal format between the 3:
1. background-color:Aqua
2. background-color: #00FFFF
3. background-color: RGB(var(--now-color_alert--info-0, 0, 255, 255))
Regards,
Vaine

[Maik Skoddow · Accepted solution]

This is the new format for styling colors in the Next Experience UI. Please check the following articles (and it's follow-ups) for more information: https://www.servicenow.com/community/next-experience-articles/all-about-next-experience-polaris-them...