You can thin a lotion with a cosmetics-grade oil, or just buy one that is thin enough to pump.

Labels are about the only thing I can think of that will prevent confusion.

I don't use pump lotion. My favorite lotion doesn't come in a pump. However my soap dispenser is always white in both the bathroom and kitchen. If I were to keep both I would make some of those beaded glass identifiers that they use for wine glasses, with a big bead in the center that I could write either an L for lotion or a s for soap. They have gold or silver pens that would work for that, just make sure the bead is not too glossy or it won't take the ink. They could even match the rooms decor.

Anyway that's my idea. If you like it then go for it

THis is off topic but since you're discussing liquid soap I wanted to share this tip I found online. Liquid soap easily gets stuck zippers unstuck. Just put a small dab on your finger tip and rub on the stuck portion of the zipper. It works like a charm.

If this is for the bathroom and you have a nice size countertop, place the soap pump really close to the sink & place the lotion pump in the center of the countertop (away from the soap pumps).

You might want to know that soap and lotion will corrode the metals on most of those pretty bottles, fast. I was replacing the NICE soap bottles in kitchen and bathrooms every 6-10 months because the metal got really yucky.
I did finally come up with solutions that worked for me but I thought you might want to be forewarned.