There are many reasons that you might want to pause a print midway and change filament or even insert objects into a cavity in your 3D print such as magnets. With flashprint and the menu's on flashforge printers it's quite easy to do this.
If you have just experienced your printer running out of filament and want to know how to prevent this. You should make sure filament detection is activated on your printer. Most of Flashforge's printers have a function to check whether it's running out of filament, but it may not be turned on. On Adventurer 4 seres to turn it on go to second page of settings and make sure "filament detect" doesn't have a little red circle symbol on it.
On the Adventurer 5 series select the information icon(bottom icon on the left side tab) to enter settings, Filament detection is a toggle switch on this screen, if it is green this means filament detection is on.
If you want to do a 2 colour print generally you have to set this up when you do the slicing part. In flashprint click "start slicing" and then in "expert mode" select the "others" tab. Scroll to the bottom and press the plus button to choose which layers you want to pause on.
If you are unsure which layer you want to pause at, you can slice the model click "slice preview" then drag the layers slider to find the exact layer you want to pause on.
Once you know the layer, you can slice again and add a pause in the "others" tab. When you print the object it will pause at that layer and allow you to change the filament.