Zazie
So 1991
This is wrong. The fact is that while the DSi has several hardware features that the DS/Lite does not, none of those features actually allow for better anything - they don't affect gameplay, graphics, or sound. The Game Boy Color could in fact do something graphically that the original Game Boy could not.
This is the fact of the matter. The Game Boy and Game Boy Color were different generations of hardware. The DS/Lite and DSi are not. You can argue if you like, but you're wasting your time.
The ability to play games in color does not equal a next gen system. If you take a look at gameboy vs gameboy color games the only difference in game play is the color graphics the graphics gameplay and sound you mentioned aren't improved by any significant amount. The only gameboy color games that were vastly superior to regular gameboy games are pokemon gold and silver and they are playable on the regular gameboy meaning that the improvements had nothing to do with the gameboy color hardware.