I have never tried this Colors so far, but if it is nearly as good as Art academy it's definitely going to be a must-buy, although I must also say a screen larger than actual 3DS one would be more convenient in my opinion.
Can you confirm this? I haven't seen the 3DS Nintendogs, but I'm gonna assume its some sort of trick like Dual Pen Sports, probably using the microphone to detect strong taps.