Brighter colors are better for survival.

[Owen]

Often depends on your surroundings, the season, etc., but any of the neon/safety/hi viz colors, whether it be green, yellow or orange is usually going to be highly visible.
You said "all conditions", though, so blue. It's not often seen in nature. Royal and electric blue are more obvious choices, but baby/sky blue actually stands out exceptionally well without being a bright color.

Frankly, visibility is not something I give much thought to, as I don't go around randomly dropping stuff, or have any trouble finding it when I do drop something.
Seems like a pretty overblown issue to me, more of a "what if" than anything.
I started pursuing outdoor activities again about 12yrs ago. Hiking, backpacking, rock climbing, mountain biking, and a little tame kayaking. I'm forgetful, and tend to misplace things, but after >100 day and night hikes, 4-500 nights in the woods, and dozens upon dozens of climbs and bike rides(2-3x/week when into them), I've lost a pair of sunglasses that were on top of my cap when bushwhacking, and a little aluminum valve stem cap that got left on the ground after fixing a blowout on my mountain bike. That's it.
The exceptions I make for bright colors are my rain jackets(rain gear being wearable shelter), for the hypothetical, but entirely feasible, rescue scenario. I use an orange one in the East, and an electric blue one out West.

 

[Katherine Alicia]

Just an idea, how about marking all your gear with a security marker instead, that way you don`t have to change the color or anything, but you can find it again easily at night with a UV light because it`ll show up as bright blue.

 

[Lynx_Arc]

You could also use reflective tape and glow in the dark stuff so you don't need a UV light along with you at all. But as someone that has lost black aluminum lights at times I couldn't find it in the daylight, luckily I looked at night and the blue in white LEDs light outputs when it hits white LED emitters you can see them glowing that is how I found one lost light. High vis tape and shrink wrap would be a big help.

 

[Stress_Test]

I had never given it much thought until years back when we had a rare, heavy snowfall event. Well, heavy for us, which was about 1 foot deep.

I had always kept my house keys and misc keys on just a ring, with nothing else. It occurred to me that if I was walking around in that deep snow, and my keys fell out of my pocket (or through a tear in the pocket), I'd be in trouble. The snow was very soft and dropped keys probably would've buried themselves without much of a trace, unless I happened to be looking at the exact spot where they hit.

I got some glow-in-the-dark paracord and tied a long tail to the key ring. (not good for snow, but that's extremely rare anyway!) In hindsight, the GITD didn't work as well as I thought. It just didn't glow long enough to be practical most of the time.

I recently switched to a length of neon yellow paracord, and that seems to work pretty well for me. It's eye catching and a bit less bulky than the GITD stuff I had before.

 

[Hooked on Fenix]

When I bought a firesteel.com Armageddon fire steel with a palm striker, I made sure to get the bright orange one. I replaced the piece of camouflage cord that held the two pieces together with Uber glow paracord. Also added a cord lock and a compass zipper pull to the cord. I will not drop it, lose, it, or get lost carrying it. I've seen enough episodes of Alone that I know if you lose your fire making tool, you're screwed. I also put an Uber glow/blue snake color milipede weave key fob on my car key. I don't want to lose my key either.

 

[Lynx_Arc]

One thing that can find car keys lost in deep snow and leaves is a strong magnet as long as you have it on a metal key ring that is steel that the magnet can grab.