Canonical tags

Hi guys,

our SEO consultant told us, that we should be using canonical tags. We have lot of clothing (like pants, shirts and so on) which are made always in different colors. Average could be like 5 colors from each product - Each color have always its own url.

He basically told us, that we should always chose one color (this color will have self-canonical) and every other color will have canonical tag referencing on the "main" color.

We will avoid duplicities this way. However that will cause, that we will lose positions for long tail keywords like "pants brand black", "pants brand brown" and so on, right? Those have probably low volume in search, but they are much more convertible.

I am not sure, what I should do, because it is like few thousand products, which will be impacted by that, which are already indexed. So I am worry, that it could have bad impact for SEO.

Could somebody tell me opinion, what is better? Ideal situation would be, that every color would have unique content, but that is not possible. The titles have to be same (only difference is color) and it would be realy hard to make some changes in descriptions, in some cases 10 times, because of 10 different colors (it is the same product after all).

Thanks a lot