Wiring light switch with neutral (Z-wave)

Unfortunately, that style of wiring -- essentially a "switched loop" -- is not compatible with "smart" switches that require a neutral.

The 2011 NEC finally recognized this and now requires neutral at switches, but your home obviously predates that requirement.

There are a few options, but none are easy/cheap:

New wire

Replace the wire between switch and light with a three-conductor (14/3) wire. You get hot, neutral, and switched hot.

New power feed

Run a new power source (which would include neutral) to either switch, and disconnect the existing source in the light.

The existing 3-wire between switches carries hot, neutral, and your signal/traveler, and the 2-wire between switch and light carries neutral and switched hot.

This requires access to one of the light boxes, as well as another power source.

Use an in-line module

Buy and install a Z-Wave "in-line" dimmer or relay in the light box to control the light.

The existing 2-wire between the light and switch would just be hot and neutral, and you'd setup the switch to control the in-line module via z-wave signalling. There is no switched-hot going to the light. The existing 3-wire between switches carries hot, neutral, and your signal/traveler.

Nice thing about this option is it doesn't require changing wiring (and thus no holes/etc). The module will cost ~$60 but that may be the cheapest option compared to the alternatives anyway.

First off -- the only guarantees found in North American electrical code are that neutrals are white or grey (but not all whites are neutral) and grounds are green, green/yellow striped, or bare. Things that are neither ground nor neutral can be any other color -- the reason black, red, and to a lesser extent blue are common is because those colors are what you get with NM cable.

HOWEVER: in a large building like your condo, the wiring will likely be done in conduit instead, which means that you won't find a ground wire (as the conduit subs in for that) and the other wires can be any color whatsoever other than green, white, or grey.

I suspect the yellow wires are hot, by the way, as there are two of them to the same screw on the switch -- that implies that the orange is switched, going off to whatever that switch controls. It's a lot harder to tell on the other switch, but perhaps the red is hot and the brown is switched? Note that a standard single pole dimmer or switch doesn't care which way it is hooked up -- the two brass terminals or black pigtail wires on the switch or dimmer are interchangeable and equivalent.

By the way, when you do put a dimmer in -- it'd be a travesty if you threw a nice, spec-grade switch with wire-clamp plates out in the garbage and put the cheapest builder-grade trash dimmer in in its place. Get a decent spec-grade dimmer from the likes of Lutron, Leviton, or Cooper; it'll stand a good chance of being move-in-ready for whoever you sell your condo to if/when you move out. (The switch is good as a spare, too, if say the next person who moves in hates dimmers, or you need it for something else.)