Coloured bar chart

Quite frequently you want to color the bars in a bar chart according to your own scheme - e.g. to highlight an anomalous measurement in red. The bar function doesn't make it easy to do this, but there is a way.
Also, only occasionally do you want the x-axis labels to be the default 1 2 3 ... So for convenience this function takes a series, a colour vector, and a list of labels.