Would being blind reduce a character’s speed?

A PC is under the effect of a Suggest spell and told to follow someone who had darkvision. The PC, who is under the effect, doesn’t have darkvision, and they are led into a tunnel system that is pitch black. How fast are they able to move?

I can’t find anything RAW which states that trying to move in darkness has any detrimental effects, other than the obvious statement of not being able to actually see where they are going.