Uh oh, what should I do?

Nothing. The only conflict technically, but will hurt nothing in your game.

Are you having problems?
If no, nothing.
My guess is that the Modular Passage Fix addresses a BHAV that exists in all modular stair packages, and that's why it's flagged; but since the stair recolors are supposed to function as normal stairs, and the Fix is intended to change the way normal stairs work, it wouldn't work on the recolors if this were not so.
If the fix doesn't seem to be working, rename the fix by putting a Z in front of LdDarcy_ . This will cause the fix to load last, so that the game will implement its code, and not the code in the stairs.
A conflict doesn't have to be a bad thing.

Thank you all for the reply. Yes the stairs from HugeLunatic work flawlessly in my game, no object error pops so far

The LordDarcy modular passage fix makes a change so that Sims can walk underneath the highest section of a modular stair, and you can place objects under lower sections without needing moveObjects on. It's obviously most useful for open underneath staircases, but it doesn't hurt for it to be in one that has supports all the way to the ground. Custom modular stairs that have the same fix use group 0xFFFFFFFF, and the Maxis ones don't, which is probably why it gets flagged as a conflict. The LordDarcy fix only changes the Maxis stairs, so there's no clash with the custom ones that have their own version.

Lots of things will show up as conflicts, some of those you might want to happen. For example, I have a bladder fix for the baby dangler, this shows up as a conflict to the baby dangle, but since I want the Maxis baby store dangler to be fixed it's a conflict that I want to happen if you kwim? A conflict is not necessarily a bad thing. The thing is do the files work in your game as intended?

The stairs from HugeLunatic still work fine without any problem till now, and so does the fix from Lord Darcy. It's safe to say that the mods go along very well. There isn't any known report when I looked up on the download pages so I was at lost. Usually the creators take notes when their hacks are reported conflicting with another like Cyjon or creators from Simbology so I know which one I should put the last. Thanks everyone for the help

If everything is working you can ignore it.