Garden lacking colour-what to plant for autumn?

Geranium Rozanne (sp?). Blue flowers nonstop from June until cut down by frosts.
Shrubby potentilla, also nonstop flowering once it gets going in early summer.
Nepeta 6 Hills Giant, clip off the first flush of flowers once they look tatty and within a week or two it'll be off again until late autumn. Needs protecting from cats who'll rub out the emerging shoots in the spring because they love it so much.
Salvias, penstomens, japanese anenomes....

Hardy fuchsia, Japanese anemone, sedum and dahlias keep colour for us into autumn. Tiny garden so no room for any others.

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Heuchera

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Rudbeckia

My hardy fuschias (Mrs Popple) flower later in the garden than they do at the garden centre and keep going until the first frosts.

I have a large clump of Rudbeckia (bright yellow sort of daisy like) that are only just starting to flower now and will flower well into the autumn. They have a tendency to spread mind you.

I also have quite a few Heuchera who’s leaves come in the loveliest of colours dark red, orange, yellow and green. They keep their colour all year around.

I’ve been working on this problem for several years.

Try Asters, particularly aster dumosus and frikartii and aster angliae (I haven’t checked the spellings, could be suspect)! These asters are resistant to mould unlike the Belgian varieties.

Japanese anemones. Can be too rampant for some people but fine if you keep them in check.

Hardy chrysanthemums - these are not the same as florist chryanths (which I hate) - and you may have to look for them online. I have a few, big clumps of bright red daisies with yellow centres. The colours are like jewels and should be far more popular than they are.

Our summer plants are just coming into their own,its been a really bad start to the season here .We lost a lot of things that this time last year filled the garden with colour .Even the phlox hasn't bloomed for as long .I'll be putting winter flowering things in early in the hope they actually flower by spring .

Have a look at helenium and sedums.
Helenium is tall (about 3 feet) and is good for the back of the border. Sedum comes in a few different varieties; we have Autumn Joy. It's quite a vibrant pink. Also good old begonias (the wax begonias) flower right until frost. I'm not especially fond of them, but have had them flowering right to the end of October.

My garden also tends to fizz out in August, so i need to add some colour as well.