I had a Kobo Libra 2. It broke and I replaced it with a Kobo Libra Colour. The biggest difference is that the Libra Colour is unusable without the backlight turned on, since the screen is so dark. The Libra 2 had a pretty white background without the backlight, whereas the Libra Colour has a grey background. I don't know if the Clara Colour also has a really dark screen or not.
It's the same, just a smaller 6" Kaleido 3 screen VS. 7". Personally I find the Libra Colour fine in a lot of conditions without the front light. Kaleido 3 is darker than BW screens but it's like bad newsprint vs. good newsprint.