TweenService is probably going to be the way to do it in as few lines as possible. You can do it with no fade in one line, because you are directly setting the color to an exact value. When you fade a color in/out you have to continuously change the color over time (basically you’re setting the color each frame along a certain gradient for a certain number of frames). Unless Roblox adds a function specifically for color (there may very well be one but I am unaware of it if so) that does the same thing TweenService does, you most likely will not have a one line solution.
Alternatively you could use a loop or bind a function to RenderStepped to manually do the same thing that TweenService is doing, but that is likely going to take more lines of code.