Wire colour matters!
Not for the current running though the wire but for troubleshooting, safety, and others that may encounter any project. At powerline level voltages, national regulatory bodies have mandated the 'hot' line to be certain colours such as red for power (and orange, black, or brown in multi-phase power) and green or green/yellow striped as the grounded conductor.
In most low voltage DC systems I have encountered, red is positive and black is negative. It is so ingrained in our designs that people will assume it on a new system, and DIY products may only say 'connect red wire here'.
When you breadboard a new design, it will not matter electrically what colours you have chosen, but it is rare for me to have completed a moderately complex build without at least one error. To troubleshoot your design is so much easier if you are consistent with what colours you have used for what part of the circuit. Colour choices can be somewhat arbitrary, but for a DC system, keep red for positive, black for ground.
In other higher power systems, or RF, the wire colour or colour banding may be a manufacturing code that tells you what the internal makeup of the wire is. It could indicate insulation type (fire resistance, voltage rating) or conductor type (aluminum, copper, steel core) or other details. I worked in designing low voltage monitoring for high power systems. I was taught that red current only flows in red wires. Let me assure you that I have seen red current happily flowing in black wires until the molten copper explodes plating the room. I then kept the red current in the red wires.
Always assume that wire colours means something if you are working on an existing device, even if all it means is that this blue wire is a different circuit than that violet wire. I have been a broke student and wired electronic prototypes with the one roll of red hookup wire I had. They eventually worked but I paid in time troubleshooting. My professional work used national electrical code wire colours in large gauge but the low voltage signals used a different colour combination, but the wires were physically different which also helped separate them. And in production, each product was the exact same to simplify the repair department work.
So for your projects the positive and negative wires should have their own colour especially since this is where you often have to connect to external power, and then the signal(s) can have a third (or more) colour. If you have a small set of hookup wire spools, you can develop your own code particular to your projects; for example, blue for inputs, yellow for digital signals, violet for analog, and green for the output side. This will help you for years to come in troubleshooting. Remember that the colour is for your benefit and adjust your rules to your designs. If you keep the project, you can write the code down too.