The funny thing is that, at least on Windows[0], there actually isn't a standard color picker. Or, well, there is, but it's one of those common-controls dialogs that hasn't gotten a UI refresh since Windows 3. People writing native apps that need to pick colors wind up writing their own color pickers[1]. Even Microsoft does this: Paint gives you the same obsolete system color picker I mentioned before, but Paint 3D ships with it's own[2].

If you ask a browser on Windows for a color picker, you get the old-and-busted one. Given the odd bifurcation in Windows UI since 8, I suspect date pickers are the same way, and the one the browser gives you won't actually match what other native apps are doing. So what happens if you decide to do the "right thing", is that you get a demonstrably worse user experience for your forms for the vast majority of people who do not know how to retheme native UI and have zero familiarity with the old Windows controls that browsers continue to throw at people.

[0] macOS has a native color picker that is apparently so good that someone reimplemented it for iPadOS.

[1] Adobe isn't even consistent among their own suite. The Photoshop color picker is entirely different from the Premiere or Animate ones, for example.

[2] I suspect the Paint 3D color picker may be a XAML default, but up until very recently the prospects of actually using XAML in most apps was very dim. More specifically, XAML used to be either exclusive to .NET/C#, or exclusive to Microsoft Store apps, neither of which were conducive to native software that need to live outside of an app container sandbox and be distributed through Steam.