Color is a format of an array. There're two types of “color” array.
[r, g, b] or [r, g, b, a]
Color - r is the intensity of red, g is the intensity of green, b is the intensity of blue.
a is alpha (opacity). An alpha value of 0 means totally transparent and a value of 1 means totally opaque. Some of the commands require/return alpha, some don't.
All values range from 0 to 1.
[0.3,0.3,0.5,1] // mauve purple
[1,1,1,1] // white
[0,0.2,0,1] // camo green
[0.73,0.24,0.11,1] // Rust orange