It always depends on the writer, and in comic books anything can be justified and retconned and generally inconsistently written. So in canon, no definitive answer can ever really be given. Although since Wolverine is the more popular character, it's more likely that some writer will make Wolverine able to pierce Colossus' flesh than the other way around.
But if you were to look at it from a scientific point of view, and transport both characters into the real world as best we could, then the answer is "probably not".
Yes, adamantium is a stronger material than colossus' skin, which is of an unspecified material but supposedly analogous to osmium. Yes, adamantium can can cut organic steel. But that's not the question. The question is if Wolverine can cut Colossus.
Just because one material is stronger than another doesn't mean one can easily use it to cut a weaker material. Think about it this way - what's stronger, steel or copper? Steel. Now take a steel knife. Try to cut through a copper penny. Did you succeed?
Take it even further. Take a steel knife. Now walk outside and try to cut down a tree trunk in one stroke. Steel is much, much stronger than wood, so you can cut the tree. But how long would it take you to cut down?
The problem here isn't that admantium isn't strong enough, it's that Wolverine isn't strong enough. Wolverine is strong, but not superhumanly strong, and since Colossus has superhuman durability able to withstand explosives and Juggernaut punches and whatnot, Wolverine is not strong enough force his claws through Colossus' armor. In fact, from a scientific sense, Wolverine shouldn't be able to cut through a lot of things he cuts through. His claws, indestructible though they may be, are retractable and anchored to his fleshy forearms with muscle and tendon. If Wolverine ever tried to cut through a material as strong as Colossus' body, what would really happen is that his claws would get caught up in the first 1/16th of an inch of Colossus' skin, then start tearing away from the top of his forearm as his tendons would not contain sufficient strength to hold them in place as his muscles drove his arm forward. It would be like trying to hammer something with a hammer whose handle is made of out of a pretzel stick. The handle would break long before the strength of the actual hammer head is tested. In fact, if Wolverine tried to cut through a thick tree, it would have the same result - his claws would get stuck in the wood maybe an inch through, then start tearing out of his forearms as he tried to drive them forward.
Even if adamantium could sharpened to single molecular edge, it still has visible width, and dividng organic steel by even 1/8th of an inch would require a strength of flesh that Wolverine does not possess. In order for adamantium to cut something that strong, the claw would have to be a plane of a single molecule wide, and this is clearly not the case with Wolverine's claws since they are easily visible to the naked eye.
The only exception I can think of is if Wolverine's muscles and tendons are also somehow admantium laced so as to be unbreakable, yet somehow still magically flexible. But other than that, the only way Wolverine could cut through Colossus would be to get serrated claws, then saw away for a long time. Which is how people in the real world cut very strong materials like steel.
Thus the weak material (and thus the first to fail) in this chain of force transfer is neither organic steel, nor adamantium, but Wolverine's fleshy body.
Thank you, that is all.