I was wondering if there's a difference between different colored wires?
The functionality isn't dependent on color (wire gauge/thickness is another matter), but...
There's some conventions that it is smart to keep to.
Red should always be the positive (eg. +9V).
Blue is 0V (often called ground), although it is very commonly being misunderstood (loads of people thing that black is the 0V color, probably because they only use single supply circuits.
Black is the negative supply (which in a single supply will be the same as 0V - it's all in what you choose to call your reference)
PC's have always used the convention of black=0, red=+5V and yellow=+12V on drive supplies (but on fans, the yellow wire, when there is a yellow wire, is for measuring the speed of the fan).
There will be no (direct) penalty for mixing up the colors - except when you can't remember which is which and burns an entire board ull of chips (and that's why it's good to follow conventions - a year or two from now you'll be glad you did if you do
Sometimes you have only one color, then it's a good idea to mark the ends of the wire with a permanent marker. I draw rings around the end, 1, 2 or 3 rings etc. and for supplies, I often tie a knot on the positive wire (both ends) and/or color the end entirely with permanent ink for ground.