In the Planner Colours section of the tool part you can configure the chart to colour code timelines depending on the value in on of your columns. In this example we are setting the colour depending on a Status column.

If you choose a column that is defined as 'Choice' column (for example Status and Priority in a Task list) then the options are filled in for you - just setup the appropriate colours.

If you have 'fill in choices' or choose a non choice based column then you will have to enter the values manually.

Click "+ Add more colours" to add an extra entry in the colour mapping table
Add the value that you want to assign a colour
Select the "..." button to open the colour palette and assign a colour to that value

In this example our Design task is Yellow (Waiting on someone else) while our Development task is Red (Not Started) - of course choose whatever field and colours make sense for your particular application.