Hmmm, I might have many different view on this.
1. Darker than the pelt
Yes, this is a good idea and works very well, but sometimes it would look off, say, if you have a strange looking character, and the paws don't look right with it, it distracts you.
2. Fully custom
This is also a nice idea, too. It'll work with your characters and yes, make them more your own, but it will also feed the people who make those bright sparkle dogs(guilty xD). Also, I get distracted easily, and seeing everyone running around with rainbow pawpads would freak me out xD
3. Brown, Pink, or black
I agree with this, since yes, it's natural colors and they're very nice choices for natural looking characters. But, say, you have a colored character that doesn't seem to fit with any of these, it can sm to look very weird and sometimes get distracting.
4. Stay how it is - One color.
Well
I would say no, well, mainly because brown isn't a very good color and it goes with very few colors, and looks strange on many characters. And, well, it looks like they stepped in.... Something else. xD