Splaying is nice, because it helps you get more icons, and that's usually a good thing. It's also one of few strategical considerations in Innovation, even though Innovation is mostly about tactics. Usually you don't want to spend time splaying unless you get a short term benefit in addition to the long term benefits, but understanding when those long term benefits matter most is important.
The black hex throws quite a wrinkle into splaying strategy. Depending on where the black hex is, some of your splay types will be messed up, some won't. It's even harder to sort out when you realize there is no perfect, ideal placement for the black hex.
There are four splay levels: unsplayed, left, right, and up. It doesn't take long to figure out that even with worst case scenario black hex placement, upgrading from one level to the next doesn't hurt you (for the overall total, at least).
One thing that is not glaringly obvious though, is the following theorem:
"For each card, exactly one of the following is true: the card reveals additional icons when its splay is changed from left to right, or the card reveals additional icons when its splay is changed from right to up."
In other words, either Invention or Railroad will improve a cards iconnage, not neither, not both. Thus, every card in base Innovation is one of two types. To most clearly convey the meaning of those types, I will call them "Invention Island" cards and "Railroad Sprawl" cards.
Remember: neither type is "better" than the other. These types don't convey how useful a card is, but it tells you
how the card wants you to splay it. An Invention Island card wants to be splayed right, and after that it is happy, it doesn't want anything more from you. A Railroad Sprawl card wants you to splay it up. Once you've splayed a Railroad Sprawl card left, it wants to be splayed up, and it has no interest in being splayed right.
Ironically, Invention is actually a Railroad Sprawl card, and Railroad is actually an Invention Island card. Try not to get confused.
I've attached a chart of what color and age the Invention Island cards belong to. Exactly one third of the Innovation cards belong to Invention Island. There are a few things to be aware of, there are a couple patterns.
1. As BrokenTree has commented before in another thread, yellow has an unusually large number of Invention island cards. The chart says red has more, but 3 of those are from age 1, which has more cards in it anyway. Adjusting for that they are even. And if you adjust for the large number of Castles appearing in low red Invention Island cards, it becomes even easier to declare yellow the king of Invention Island.
2. Blue goes an astounding 4 ages without a single Invention island card, the longest streak of any color, and its the first four ages. And there's actually only one streak of 3, which doesn't really count because the streak includes Age 10, which rarely is covered. So splaying blue left early on can pay off in the early game, you won't get the urge to upgrade from left to right anytime soon.
3. Age 4 has the fewest Invention Island cards, but it is immediately followed by age 5, with the most. The invention effect, itself, belongs to age 4, but won't be very useful on covered 4's.
If you've only covered up 1's, 2's, and 3's around the time you get Invention, you're looking at 5 red cards that can benefit from invention, 4 yellow cards that can benefit, 2 green cards, a purple card, and no blue cards whatsoever. One moral of the story is that Invention is a pretty troubled card, stuck improving a stack of red cards that will yield you icons of a probably irrelevant type, or improving the yellow pile that can splay itself on its own with Reformation. Perhaps a more useful moral of the story is that it might be a wise idea to spam Experimentation before returning to Invention later, since age 5 has the most Invention Island cards.
4. All other things being equal, select Purple for Feudalism, Purple for Industrialization/Emancipation, and yellow for Publications (blue tries to overcompensate for its strange behavior in the first four ages later on).