just some quick comments. not mean to discourage you but ur comments says u're really v. new
. basic photography skills is all tht's needed fren.
1st pic, i dunno wht's d-lighting, but pictures with such bright background, you've 2 choice. use fill-in flash or sometimes wht i do is over expose the pic +1 to +2 and blow out the background if its not interesting (anyway). (i know, most ppl dun agree with me, but i'm just a tourist for such things)
2nd pic grainy coz high ISO. flash will NOT help you here. in fact, if u had used flash, this picture can throw away, coz u'll not see anything in the background. best advice - USE A TRIPOD and low ISO and DROP the flash idea. go down ur flat/condo/house at night to try this out to get a basic understanding of how ur camera behaves at night.
3rd pic, wht do u mean by color not as sharp? u mean picture not sharp? remember the unsharp mask advice. all DSLR needs to do it.
and by the way, 90% of the time, i use aperture priority, no need to switch mode here & there, no point at all. the other 10% of time are unique situations, eg. fireworks etc