BLB color codes are the same as colorset color codes.
Both of those are just RGB (Red, Green, Blue).
The last number is the brightness on a scale of 0 to 1.
RGB is measured on a scale between 0 and 255.
If you notice, the BLB is measured on a scale of 0 to 1.
If you take any RGB number and divide by 255, you get BLB.
So, the RGB color, "108 45 199," or purple amethyst, would be
"0.423529 0.176471 0.780392 1," rounded to 1,000,000th.