Grouping similar data/images
Try t-SNE (http://lvdmaaten.github.io/tsne/), it can help you group pictures that have the same properties via dimensionality reduction. You can see an example here http://cs.stanford.edu/people/karpathy/cnnembed/ where t-sne is applied on various imagenet samples.

This will group images with similar content close to each other (dogs near dogs, black dogs near black dogs...). However, if your black dog is yellowish because of the lighting, i suspect it will not be close to the same black dog under normal lighting condition. For that, maybe you can try black and white pictures? or add a black &amp; white layer on top of your RGB input.

I did not experiment it myself, but you may also want to have a look at DeepBit http://www.iis.sinica.edu.tw/~kevinlin311.tw/cvpr16-deepbit.pdf "an unsupervised deep learning approach to learn compact binary descriptor for efficient visual object matching".