A cart that integrates with existing site and handles various colored products easily

This seemed a good place to ask this question. I am looking for a shopping cart for a client and have not found the perfect match.

Requirements:

1. A shopping cart with a wide range of supported checkouts
2. Should be able to handle various colored products well
3. Should easily integrate with an existing site

1. Is pretty self explanatory it should support the big gateways in the game.
2. The client in questions sells a range of custom clothing and footwear, in a wide variety of colors. So first prize would be images/thumbs generated base on the selected color. Second prize would be a robust color swatch system that puts the item of correct color into cart. Open to ideas beyond that if people have seen or used great solutions.
3. Although I am aware opencart as example can handle this task, I have issues with open source software. I also want something that integrates with existing sites. Secondly where as one can debate what converts better and it will likely make for a great topic, most store front solutions are very limiting in design options. Especially onces the developer steps away and leaves the client to manage the site.

My weapon of choice is usually Ecwid as it allows for a variety of pages, the client to have freedom to create these pages and then just insert some predefined html into the page to add the shop. Unfortunately it lacks the features to really deal with the variety of colors, so I am fishing for new ideas.
Many thanks to any one who takes the time to make a suggestion.

I believe that Ecwid is the best solution for you because only it can be integrated easily with an existing site.

You are partially correct, Ecwid is an awesome option and can manage the task. Sadly it requires the most expensive package and a complex setup process to approach the required functionality. If nothing else can be found I may have to go ahead with it, but its not the best solution for the client who will be using the site.
Thanks for your input though, maybe someone else will find something I have missed or a share a gem.

Even i agree with slowdive. Ecwid is overall very good option but due to its high packages, very few can afford it so many have to switch to other available solution.

Have you looked at Magento? It's very powerful, but not sure if it has the color options you're looking for though. I bet there's an extention you could get for adding color options to items to Magento. Good luck in your search.