Distance is not a good measure of 'distance' in space travel
Pluto is 7.4 billion km from the Sun at aphelion, and 4.4 billion km at perihelion. Neptune, the next closest planet is between 4.4 and 4.5 billion km from the Sun at all times. What this means is that there are times when Pluto is about 7.5 billion km from Earth; and there are times when Pluto is over 11 billion km from Neptune. The planets are all moving in relation to each other. The distance between two objects varies over time; the straight line distance at any given time has little to do with how hard it is to get from one planet to another.
An object set into motion will stay in motion, says Newton's laws. In order to move from one place to another, you need to generate enough velocity to break out of one orbit and insert into another. These are usually called 'burns' from burning a rocket engine, and are best described in terms of delta-v, the total amount of velocity change needed to move from one orbit to another. The delta-v is in turn proportional to the amount of fuel (energy) and propellant (reaction mass) needed. Energy and reaction mass are the true quantities in which 'distance' in space should be measured.
To get from one orbit to another, you need a transfer orbit. A commonly used one is the Hohmann transfer orbit, which is the transfer orbit using the minimum amount of energy. On the other hand, a transfer orbit that yields a seven day travel time will take a lot more energy burning. But, the relative energy it takes to move from planet to planet will stay roughly the same.
As it turns out, due to the shape of the orbits, the Hohmann transfer delta-v to Pluto is less than that to Neptune. Further more, the delta-v to Alpha Centauri, or any other point outside of the gravitational pull of the Sun is about 12.3 km/s, which is marginally more than the 11.7 km/s delta-v to Neptune. So, if you have enough fuel and propellant to get to Neptune, you pretty much have enough fuel and propellant to get anywhere you want. Of course, at some point you have to worry about the Milky Way's delta-v, but the travel times to stars at sublight speeds mean you have bigger problems than just fuel and propellant.
You don't 'run out of fuel' in space travel. You have a set budget of energy and reaction mass, and you burn that to get into transfer orbits. Presumably, you should burn into your transfer orbit, then spend days to months (to years) coasting to wherever you wanted to go, depending on how much energy and reaction mass you burned in the first place.
The minimum energy and reaction mass needed for a given burn are well established, withing the solar system. Any craft headed to Saturn (10.3 km/s of delta-v) or beyond has close to enough energy and reaction mass to make it anywhere within the gravitational bounds of the sun. So the answer to your question is: If you can colonize Pluto, you can colonize anything in the Solar System