Some colors are just better at some things at others and when colors get things that aren’t in their normal strengths, sometimes even those “leftovers” are good enough for a cube.
Harmonize is a really good example. It was a “planeshifted” copy of Concentrate, a card that has fallen by the wayside in many cube lists. But Harmonize doesn’t suffer from that fate as many green cube sections feature the 4 mana sorcery. Why?
Harmonize plays better to green’s strengths and weaknesses better than Concentrate does to its strengths and weaknesses. While green gets card advantage through cards like Krosan Tusker, Yavimaya Elder and Life from the Loam, green tends to not have much in the way of pure card draw, while blue very much does. Green decks tend to not care as much about keeping mana untapped on the opponent’s turn (although cards like Vines of Vastwood are used in that way) whereas blue decks use instants far more often than green ones, so Harmonize‘s sorcery speed isn’t as much of a drawback for green mages as much as Concentrate‘s sorcery speed is for blue mages.
Sunlance is another example of this kind of card – it was a planeshifted version of Strafe, a suboptimal removal spell in a cube’s red section, but it’s a solid card in a white commons section since white has so few removal options at common for 1 white mana (Kirtar’s Desire being one of the few other options.) Since red has much better options like Flame Slash and Lightning Bolt, it doesn’t need to bother with Strafe, but Sunlance fits white like a glove.
Kor Sanctifiers was a card that I initially thought was weak because it paled in comparison to its green counterparts. “Green can kill artifacts and enchantments too and gets a 4/4 for 1 more mana with Wickerbough Elder and Indrik Stomphowler! Boo!” Of course, this doesn’t address the fact that while green has those two cards to Naturalize things, white doesn’t have those kinds of options strapped to creatures. It may get enchantment removal through cards like Kami of Ancient Law, but artifact destruction tacked onto a creature isn’t too common in white. My foolish statement also ignored the fact that in general, cards that can deal with multiple things are pretty strong since the threats in a cube are so varied. Mimic Vat, Control Magic and Sylvan Library are pretty varied in why they’re powerful, yet all of them fall to the power of Kor Sanctifiers.
Of course, there are limits to this rule. Gate to Phyrexia may give mono-black decks ways to deal with artifacts, but it’s a really bad one and you should never cube with that card. Keeping colors’ strengths and weaknesses in mind is another vital part of card evaluation, especially for cube and its sections.