Not just colour but mostly. I assume that the colour comes from mashing different coloured grain and so they will likely have a little more flavour the darker they are.
But really, the big win is in malt flavour and body (rather than any roastiness or chocolate notes) and mouth feel.
If you really want to add those roasty chocolate or other flavours from malt, you would want to steep some special grains and add that with the water to your kit.
For example, I wanted some chocolatey flavours in my kit based RIS so I steeped 300g of chocolate malt and chucked that in...
...even at 10.5% ABV you can taste those roasty, choccy, coffee flavours coming through! :thumb:
This is where kit brewing starts getting really fun!
EDIT: missed the question about liquid malt. I'm not sure that it does taste any better TBH. I've just had better success with it so I'm tending to stick to it. All the beers I've done with it have come out really really good. That and the fact that Rob does it at 4.40 per kilo makes it not much more expensive than dried. :thumb: