i heard that on sunny blue sky days you go for a dark underbelly lure to contrast the sky and the opposite on dark, overcast days. can anyone expand on that.

here's what it comes down to...  nobody really knows why certain colors work at certain times... just because a fish sees something, most certainly does not mean it will bite. 

watch a pro tournament, does every pro use the same color in the same area? absolutely not.  So that tells us, one of 2 things.  1) Color doesn't matter  2) If the top elite pros in the world can't figure out when and why to use certain colors, the average angler shouldn't even bother attempting.  Focus more on your presentation.

Most everything in the water that bass feed on has a white belly.  Anything with a white belly (the bass don't see the top of a topwater lure anyway), is good.

I've always used black/darker colors on cloudy days, and white/lighter colors on sunny days. While some day's, they'd go for it regardless of color and condition, others they would only hit them if I went by that. I'm not sure who taught me that.. But it seems to hold true for me part of the time.

I agree with the typical rule of thumb:

White or Flashy on sunny days

Black or Dark at dawn/dusk or cloudy days

A lot of times we get fixated on how the lure looks in the water from our perspective. I remember reading an article on why black is good at night - the author described holding your lure up and looking at it with the moon behind it and that's what the bass see.

Generally speaking, this is a good starting point.  Dark profile on dark days, dark water.  Light on bright days, clear water.  Natural colors and shades mostly.

I've had good luck with silver, bone, and smoke colored topwater plugs.

you didn't specify what topwater type bait you are asking about but for most of my top water presentations with treble hooks i use shad colored baits . the only time i use something different is when i throw trout patterned waking swimbaits .

watch a pro tournament, does every pro use the same color in the same area? absolutely not.  So that tells us, one of 2 things.  1) Color doesn't matter  2) If the top elite pros in the world can't figure out when and why to use certain colors, the average angler shouldn't even bother attempting.  Focus more on your presentation.

I don't think color doesn't matter its just a smaller part of the equation. I would put much more emphasis on presentation.

I would say dark baits in low light and lighter colored baits on bright days are the higher percentage options but not the rule.

Bone 

Your favorite color will work just fine.

8-)

K.I.S.S.   white, black, and clear.

I think when it comes to topwaters, sound is more important than color. Bass will hear or see something trying to escape and their instinct is to eat it, not look at the color and decide if its the right color.

i just fish anything natural.

This is the lure i use the most. The white belly gives it the most natural look. I also like to use a light shade of chartreuse when the bite is hard to come by. 

90% of the time I am fishing with black on the top.  The only exception is frogs, I do use a lot of greens and whites with frogs...Not sure why, guess it is confidence.

More and more I go by the Mr. Fords rules on color, just change the wording a bit.  You can have your topwater in any color, as long as it's black.  90% of my topwater fish of all species come to black lures.