[R] lattice question

[Troels Ring]

Dear friends - I have a plot of simulated data to compare to the 
observed and want the simulated to appear accumulated so that a darker 
grey corresponds to more lines of simulated data, but on top of that I 
want the measured values (Na) to be very visible. The code below meets 
only few of the desires. Hope someone will give me help to master the 
panel formation.
Best wishes
Troels

xyplot(Na+yrep[,1:100]~time|as.factor(ID),yrepbug,type=c("g","o"),
span=0.75,ylab="[Na]")

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Troels Ring - -
Department of nephrology - - 
Aalborg Hospital 9100 Aalborg, Denmark - -
+45 99326629 - -
tring at gvdnet.dk