The question was: "I intended to make paint_ramp to paint the different high B-values in different colours. But my special wish was, to pretend for a special B-factor range a self- selected colour, say B from 0-20 blue, B from 20-25 violet, B from 25-30 red, B from 20-30 yellow .... I tried the same thing with paint_prop, but I was only able to say B > 20 but not b > 20 and b < 25 simultaneously. Do you know a answer ? I was able to get a reasonable coloured chain - this was not the problem - but my results looks more convincing, if the B-factor ranges and colours could be selected individually."

The easiest way is to use paint_case use something like:

 pa_case atom_b > -1.0 blue
 pa_case atom_b > 20 violety
 pa_case atom_b > 25 red
 pa_case atom_b > 30 yellow

etc. You may want to put this into a macro if you do it more than once.