Depending on the density of the weave, color may show through. It all comes down to what you buy. A heavy/tight weave is going to be more expensive due to the increased material cost, but little to no color shows through.
I have no idea why someone would say that you need to wrap the wire in tape, unless they mean in the way it aids the installation of sleeving onto large bundles of wires; which is true. You don't leave the tape under the sleeving for the final installation. That would look horrible and waste a ton of materials.
The total sleeving cost will simply be the length of each wire added up. For example, if there was 24" of wire on the 24 pin ATX connector, you'd need 48 feet of sleeving if you did the wires individually. As you can see, this will add up quickly.