Copyright? No. Trademark? Yes.
Christian Louboutin recently won the right to trademark its red heels, spurring questions about what else can be branded.
Well, actually, a lot else—sounds, shapes, symbols, and even colors can be trademarked.
Don't confuse the term "trademark" with ownership of color though. Trademarking a color simply allows a company to use a particular combination and shade of color in its own industry. Source.
To specifically address your question — No, even if the legal small print on the site had clearly stated you had to identify them to use any color or combination of colors found on the site. No one can "own" a color and color cannot be subject to copyright. But it can be subject to attribution and legal rights.
Color is subject to trademarks. And that's important for you to know as a graphic designer. It isn't the color per-se that you need to worry about, but why and how you're using the color.
For example, if Suretape Technologies LLC hired you to design a new logo for a line of painter's tape they were making and you chose to use purple, you'd have trouble. The color is a trademark of 3M, who also manufactures painter's tape. 3M's a particularly good example, as they also own a trademark for canary yellow, which they use on their PostIt® notes. But those examples are important. One cannot simply "trademark" a color — people and businesses must trademark the use of the color. Thus, if UPS can trademark the use of brown for their delivery vehicles. Can a car be painted brown? Sure... until you slap "Liberated Courier Delivery" on the side, then you're open for a lawsuit.
Should you lose sleep over it? No. Trademark protects a company from infringement by competitors. And while some companies go berserk protecting their marks (famously, WordPerfect sued any software company using the word "perfect" in a product or company name), most of the time you need only worry when it comes to direct competition.
But, this is still one of the many things you, as a graphic designer, should keep in mind. Graphic Design involves, with regret, much more than graphic design. If a major corporation hires you to create something, it would be prudent to discover (by asking that company's legal department) what colors are trademarked by competitors.