The trend in industrial automation these days is to use grayscale graphics for most HMI elements and use color to indicate alerts and alarms. The theory is that an experienced operator can navigate and view everything they need for normal operations just fine without color, and abnormal conditions will be stand out as they're the only things with color on the screen.
It seems to work, and I encourage my front end guys to follow that pattern, but I'm not sure how well it would translate to desktop computer use.
This reminds me of a depressingly common mistake in web design that seems to affect almost every internet banking system and most government web sites. You know the one: having an "inbox" of automated messages with a number in the corner, which you slowly see tick up as you check the website a couple of times per year for a decade or two.
It's the most user-hostile web design imaginable, far beyond just being ugly or unclear, because it creates busywork or stress or both. It's effectively saying that you might have an actually important update to read, but you won't know that unless you sit down to read dozens of automated messages to sift through them; and if you don't have time or motivation to do that right now, you're left wondering if you're making a mistake that might cost you down the line, especially when it comes to many of the kinds of websites that choose to do this.
If you actually want a user to take action, you need to tell them that front-and-center in the first page after the user is authenticated, and design cues like size and color can help with that. A truly serious matter can put a modal in the flow. They have no problem doing this for the triviality of requiring you to change your password "for your security"[1], but a message about possible financial consequences is unread message #73.
[1] They had a breach they hope you don't know or care about.
It seems to work, and I encourage my front end guys to follow that pattern, but I'm not sure how well it would translate to desktop computer use.