To start go to the 3 lines menu in the top right hand corner and choose 'Custom fields'.
Then select 'Add target field' from the top of the page.
After you have named your field, scroll down and find it in the list. Then click the pencil icon next to the name.
You can then select target type 'automatic' and compare any two grades you have as an aspect.
If you tick the background box (furthest right), the pupil cards will then automatically display their on/below/above target colour.
If you choose 'Manual' from the pop up box under 'Target type', you can decide what colour each pupil's card is. You must tick the field as 'visible' and as 'background'. You can then click the pencil icon on the legend within the class and tick the Coloured Circle that will be on each card which will cycle through the different colours.