I have not noticed a difference in play during different days, nor during different perks.
I started almost 3 months ago, so never experienced the nirvana of the easy cards days, but to be honest, the game hasn’t been all that difficult, I found. Certain levels and zones were annoyingly difficult, and then you get the 30 minutes of free play, 30 minutes of momo or 30 minutes of golden tiki and life gets a lot easier.
So now a part of my strategy is to play certain zones based on when the various 30 minutes of free play show up. And with @CindyLu 's new handy dandy list Daily Bonus Rewards list
… Good times.
And to echo Papillion, my time on Tripeaks Solitaire (TS) can be divided into 2 phases. BP6 and AP6, before and after I first experienced the joy of Perk6’s golden tiki. BP6, TS llfe is pretty much as you state it, a black and a white drab, AP6 is the Land of Oz.