To customise the colours in a chart or graph, go to Dashboards (top bar)> three dots (top right of the chart to be edited)>Configure Chart. With the top section set at Chart Series (default position; on the left), click on the coloured box to the left of the data name box (top row of the series editor).  Select a colour from the dropdown menu or type in your preferred Hex number. Save your changes (top right of page) and Exit (top right).