In YNAB you can flag a transaction any one of six colors (or leave it unflagged). The flags cannot be named though. You can assign a significance to a color but there’s no way to document your system within YNAB itself.
The Set Custom Flag Names (with Tooltips) setting provides the ability to set custom names to flag colors. And if you can’t remember what Blue was meant to signify, hovering over a blue flag results in a tooltip that displays the name you assigned.
However, note the warning the Toolkit developers provide with this setting: “Custom flag names are stored locally in the browser in which they are set and will not be carried over to other browsers/computers. Custom flag names will be lost if browser data is cleared.”
This Toolkit setting has a very high “cool” factor and I know some YNAB users develop very complex systems using colored flags. I’d hesitate to build any type of system I might come to depend upon with this setting given the fact that the flag names can easily be erased from your browser memory and they can’t be synced across multiple machines. Even if you’re not depending on the flag names, I’d caution against critical systems built on colored flags. I recommend building any significant systems using the memo field instead.