Does Attaching a Flash to camera take better portraits?

[soldier]

Because I am having problems getting to the forum page, I am sending my same request again to ensure it is delivered.

I have a Canon EOS 50D camera. I do also have a Canon speedlite 580EX. My all Canon lens in my possessions are: 28-135; 17-85, 50 MM, 1.8; 28-105; and
70-210 lens.

Christmas holidays is just around the corner. Colorlful and bright Christmas trees will be found in my Church sancturary, you also find them in the shopping malls.
I'd like to take family portraits in front of the Christmas tree with my speedlite 580 EX attached to my Canon 50D. All my shots will be at night. I presume in the church sancuatry lights will be of the flourescent type.

Does utilizing my speedlite will take colorful and beautiful portraits?

If so, what lens (the ones mention above) and camera settings would be best at night portraits?

Since I am having a difficult time getting to the forum, please send me a copy of your response to Smlsaimin@aol.com

Thank you