First, type "fx_lightsaber" into the search bar and find the lightsaber you want to change, the file we're looking for has to be an EffectBlueprint and has to end with a color.
For this example we will use darth maul.
First we will change the color of the glow/reflection, head to object>components>1>light and find the "color" value. the max number here is 5. X = RED, Y=GREEN, Z=BLUE. Pretty simple, mix and match to find the color you want.
Now head to object>components>0>emittergraphparams and try to find these vector parameters: 718108376 = Outer Color | 1702781104 = Inner Color | 31253465 = Width, Length, Trail Strength | If they do not exist, then create them and add your own values, and make sure "W" is set to 1.