Colour

In the above screen shot, you can see small, gray and coloured boxes to the right of the listed tasks. You'll notice that the top 3 tasks have different colours than the rest (red, navy blue, light blue).

In this case, the colour is used to "attract attention, group elements...[and] indicate meaning"as the coloured boxes indicate the priority of task it sits beside.

The RTM colour legend is as follows:

Priority 0 (No Priority) - Grey
Priority 1 - Red
Priority 2 - Navy Blue
Priority 3 - Light Blue