GnuPlot - 2d-graph --> depending from size, different color

Hi,

i would like to change color depending from the valuerange.
a gnuplot-script will generate a multiplot and in one graph,
the ranges should have different colors, e.g.
100 ... 133 --> red
200 ... 233 --> blue
300 ... 333 --> orange
400 ... 433 --> green

#Partikeldata - Partikel INDEX  - [ 4 ]
set size 1,0.17
set origin 0,0.32
set format x ""
#set key left Left bot font "Helvetica,8" 
set noxlabel 
#set log y
#set mytics 10
#set grid mytics linestyle 0 linewidth .8
set yrange [50:450]
set ytics (100,133,200,233,300,333,400,433)
#set format y "10^{%L}"
#set grid x
set key left Left bot font "Helvetica,8" 
set noxlabel 
set label 1 "Partikel-INDEX" at graph 1.0, graph 0.5 rotate by 90 center offset 1,0 font "Helvetica,8"
set cbrange [100:433]
set palette defined (0 "blue",17 "#00ffff",33 "white",50 "yellow",\
    66 "red",100 "#990000",101 "grey")
plot "${Home}/scripte/index.txt" using 1:(\$2) t '   PD < 0,532 �m' w p pt 6 ps 0.2 lc rgbcolor "#999999"

I tried to solve it with the blue colored "set range / set palette" but it didnt work - all the generated dots are red. Can somebody help me?
Thanks in advance!
IMPe

What I usually see done for this is plotting different graphs for different values, making mathematical functions that exclude the data above and below certain values (i.e. making it discontiguous).

Another option would be using pm3d, which would let the colors change smoothly. But using pm3d pretty much means you're doing everything freeform 3d, and have to start worrying about whether your polygons are thick enough to be seen as lines etc.