Hello Paul,
Thanks for your question to the forum.
There are a couple of plants that immediately come to mind and meet all of your criteria regarding colour, quick growing and low maintenance.
The first is an ornamental grapevine called
Vitis coignetiae. This grapevine has non-edible grapes but it is the foliage that would be the talking point if you selected this plant to grow on the pergola. The leaves are large, heart shaped, shield-like with prominent veins.
The colour comes in autumn when the leaves provide a magnificent display of bright reds, oranges and purples.
Vitis coignetiae will grow quickly, each stem reaching 20-30 metres in length. No pruning is required except to contain the plant when it gets too big. It also self clings using tendrils so you will not have to do any support work apart maybe from tying in the leading shoot to the structure once planted.
The other climber I had in mind is
Parthenocissus tricuspidata. Again self-clinging, this plant has other similar qualities to
Vitis coignetiae and both plants will give their very best autumn displays on your south-facing site. Please note both plants are deciduous so you will have some leaf clearance to do and the stems will be bare in the winter. Maybe you could plant one of each plant at either end of your pergola for double quick coverage.
For more information about Parthenocissus tricuspidata see our plant database
Hope I have been of some help,