The Red drives were always NAS units, the purple was surveillance. Are you thinking of the Blue line, which is the "cheaper black" units? Those are terrible drives, I just toss them when I get one. Every one I had would lose it's format or have other weird issues.
As far as the green units, there's nothing wrong with them for data storage. The main difference is they rotate slower, and consume less power. The big problem came from the overly aggressive head parking, which was something like 10 seconds of inactivity. You'd wind up with a drive that parked thousands of times in 6 months, and it would die. I went through probably a half-dozen of those in a year before just getting them RMA'd once more and selling them.
Toshiba was the other manufacturer I was thinking of, not Hitachi.
I have messed the colors. Still, I wouldn't trust a red, purple or green due to their marketing towards a specific use that doesn't make sense to me. I wouldn't rule out a Blue for casual use, but I would go for Black or Gold if I wanted reliability and some heavy operation.
I don't trust the Toshiba drives, they don't fail at spectacular rates but they can be finicky, hopefully their more expensive line might be better.
The older Reds were fine, I've had plenty of those running for 5+ years, but I wouldn't trust the new ones with potential SMR except in single drive applications with no kick-out.
The spin rate of the red drives tries to balance speed with power consumption, no head parking, and specific error recovery rates and timeouts that are known so a RAID controller doesn't kick them. Never cared about the other ones, so who knows.
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