I used to use this all the time. I find it so hard to choose colors to unite multi-photo layouts and I loved uploading a collage of photos to Kuler for suggestions.
Last time I looked the whole site had been rewritten and the photo upload option was gone.
I'm so glad to see it back
ETA: If that doesn't work, try this link https://kuler.adobe.com/create/color-wheel/ and then click the camera icon top right.