[pstricks] Precision of dimensions/colors

[Grzegorz Owsiany]

In my application i convert rgb colors from range of fields: [0..255].

e.g. red = [255 0 0] gives [1 0 0] in pstricks rgb color mode.

I'm using my own arithmetic which can represent proper fractions with
precision to n-th digit after decimal point.
if n>9 for rgb colors latex sometimes stops with error.
What is the most accurate and precise color mode in pstricks?
Now I'm using rgb and gray modes. Does using n=9 precision have sense
for representing colors?

For dimensions i use 1cm as a unit. I suppose that 1pt will be more
accurate because pt is basic unit in postscript, am I wrong?