Assuming that your laptop display is the common liquid crystal type, there probably is not a contrast adjustment. The "crystal" in an individual pixel element can be on or off, but there's no such thing as x% on. The only adjustment many of them have is brightness of the backlight. Some plasma displays may have other adjustments; but they're often inaccessible, and usually given misleading or incorrect labels if you do find them. Plasma displays do appear, but the LC type are much more common.
The only thing that should be "flashing a message" from the task bar is one of the icons in the toolbar. Such "notices" should only come spontaneously from the bar at the lower right, sometimes referred to as the "System Tray" or as the "Startup" bar.
All of the icons there should be associated with running processes, since the reason they're there is that they start when you boot the machine AND they are processes that you can "edit" or make responses to.
Processes that start at boot but that have no adjustments or responses you can make normally are not shown.
Icons there can be associated with a number of individual "processes" shown in Task Manager, so looking at Task Manager often is rather uninformative about what goes with which icon.
The most likely cause for a brief flash notification is that a process that you could have made an input to was doing something, but a default setting allowed it to proceed so that you didn't need to respond. The most common event that will cause this to happen could be that one of your processes "needed to call home" and the connection was open. It could also happen if one of your processes, such as your AV program, completed downloading an update. You could have been asked whether to install, but probably are set up to allow automatic installation of updates. In this case the "flag" might pop up when the download completed, but would disappear when the preset "permission" to install was found.
Occasionally a "new icon" will open in this tray, and will disappear as soon as it's done its duty. Even if you can't catch what's on the flag, you'd likely catch the expansion of the bar length to make room for the new icon, and/or contraction when the icon disappeared, so if you haven't seen the bar itself "pulse" this way it's most likely one of the regular running things.
This is all just guesswork, of course, unless you can pin down precise times when it happens and associate the happening with something else that is happening.
It's an indication, probably, that your computer is just doing something it's supposed to be doing; but it's like when the kid say's "Look Ma, I ate all my brocolli." Until you confirm what's been going on, you don't really know the brocolli's inside the kid and not outside the window or in the dog. But computers are probably more reliable than kids (my kids anyway).