title: ggplot change fill colour without losing colour gradient
body: <p>Maybe this is a very basic question but I'm a ggplot and R beginner.</p>
  
  <p>I'm using this command to get a barplot:</p>
  
  <pre><code>ggplot(data=melt, aes(x=variable, y=value, fill=value)) +
    geom_bar(width=.8, stat="identity") +
    xlab("Samples") + ylab("Expression") + ggtitle("Gapdh") + 
    theme(plot.title=element_text(face="bold", size=12)) +
    theme(axis.text.x = element_text(angle = 45, hjust = 1, size=10)) +
    theme(axis.text.y = element_text(size=10))
  </code></pre>
  
  <p>I want to change the colors of barplot, but keeping the gradient of the colors depending on value column. I've tried this but I lose the gradient:</p>
  
  <pre><code>ggplot(data=melt, aes(x=variable, y=value, fill=value)) + 
    geom_bar(width=.8, stat="identity", fill="red") +
    xlab("Samples") + ylab("Expression") + ggtitle("Gapdh") + 
    theme(plot.title=element_text(face="bold", size=12)) + 
    theme(axis.text.x = element_text(angle = 45, hjust = 1, size=10)) + 
    theme(axis.text.y = element_text(size=10))
  </code></pre>
  
  <p>The data is simple, only two columns( variable - value ):</p>
  
  <pre><code>variable    value
  1   nu73    13576.49
  2   nu73t   10891.88
  3   nu81    12673.33
  4   nu81t   12159.91
  5   nu83    12570.82
  6   nu83t   11828.04
  </code></pre>
  
  <p>Thank you guys in advance</p>