Gradient Fill in Bar Graph

I'm looking at behavior of different groups of people (called Clusters in this data set) and their preference for the type of browser they use. I want to create a bar graph that shows the percentage of each cluster that is using each type of browser.

Here is some code to generate a similar dataset (please ignore that the percentages for each cluster will not add up to 1):

browserNames <- c("microsoft","mozilla","google")
clusterNames <- c("Cluster 1","Cluster 2","Cluster 3")
percentages <- runif(n=length(browserNames)*length(clusterNames),min=0,max=1)

myData<-as.data.frame(list(browserNames=rep(browserNames,3),
                           clusterNames=rep(clusterNames,each=3),
                           percentages=percentages))

Here's the code I've been able to come up with so far to get the graph I desire:

ggplot(myData, aes(x=browserNames, y=percentages, fill=factor(clusterNames))) +
    geom_bar(stat="identity",position="dodge") +
    scale_y_continuous(name="Percent Weight", labels=percent)

I want the fill for each cluster to be a gradient fill with high and low values that I determine. So, in this example, I would like to be able to set 3 high and low values for each cluster that is represented.

I've had trouble with the different scale_fill commands, and I'm new enough to ggplot that I am pretty sure I'm probably just doing it wrong. Any ideas?

Edit: Here is a picture of what I'm looking for:

(Original image available at https://www.dropbox.com/s/py6hifejqz7k54v/gradientExample.bmp)

Is this close to what you had in mind??

# color set depends on browser
library(RColorBrewer)     # for brewer.pal(...)
gg        <- with(myData, myData[order(browserNames,percentages),])
gg$colors <- 1:9
colors    <- c(brewer.pal(3,"Reds"),brewer.pal(3,"Greens"),brewer.pal(3,"Blues"))

ggplot(zz, aes(x=browserNames, y=percentages, 
               fill=factor(colors), group=factor(clusterNames))) +
  geom_bar(stat="identity",position="dodge", color="grey70") + 
  scale_fill_manual("Cluster", values=colors, 
                    breaks=c(3,6,9), labels=c("Google","Microsoft","Mosilla"))

# color set depends on cluster
library(RColorBrewer)     # for brewer.pal(...)
gg        <- with(myData, myData[order(clusterNames,percentages),])
gg$colors <- 1:9
col    <- c(brewer.pal(3,"Reds"),brewer.pal(3,"Greens"),brewer.pal(3,"Blues"))

ggplot(gg, aes(x=browserNames, y=percentages, 
               fill=factor(colors), group=factor(clusterNames))) +
  geom_bar(stat="identity",position="dodge", color="grey70") + 
  scale_fill_manual("Cluster", values=col, 
                    breaks=c(3,6,9), labels=c("Cluster1","Cluster2","Cluster3"))