It's even more restricted for the brand. If you trademark "sky blue" then you'd have to prove that consumers have a strong association between the color and your brand. And even then, other brands can still use "sky blue" in their branding as long as they're not competing in your industry.
People often bring up trademarking colors as crazy but I actually think it's one of the more sensible parts of IP law.
I agree that trademark law is generally pretty sensible.
It's worth noting that it's pretty expensive to trademark something, and you need to keep paying to keep your trademark. As a policy this is sensible for something the depletes a "commons" like words or colors.
(It's possible to argue that trademarks aren't expensive enough for some corporations. But for the costs are a significant disincentive to just go trademarking everything)
If you haven’t filed for state or federal registration, your trademark protection is based solely on using your trademark in commerce within a particular geographic area. This limits your rights, as you can only enforce your trademark rights for the specific area where your trademark is used.
People often bring up trademarking colors as crazy but I actually think it's one of the more sensible parts of IP law.