if you bealive that a full vision rider can't control his controlled and trained mount on dark. I'm ok, but I strongly disagree.
ask your DM before do it.
As in tell it what to do, yes. As in make it do it flawlessly as if you were its familiar and it could see through your eyes, no.
How about this. Let's say you cast Dominate Person on a creature who is blinded. According to the description of the spell you have "precise control" over the target.
So if you command that dominated person to attack another creature, does it have disadvantage because it is blinded or does the fact that you are "controlling" it change it so that it is no longer blind?
Let's take this a step further. Let's say an enemy sorcerer has the spell dominate person and devils sight he casts dominate person on one of his own soldiers and sends that soldier into attack you inside your sphere of darkness. Does the soldier have disadvantage to attack your warlock? After all he is being "controlled" by someone that sees you.
Just because you are "controlling" the mount does not mean you are moving its legs!
Finally, RAW in order for a creature to be a mount at all it has to be "willing". If it is not willing you can not control it like a mount. Do you think it is safe to assume it is going to be willing to continue being your mount when you blind it?