The strong force, as you may or may not already know, is the force that holds protons and neutrons together. The unusual thing about it is that its magnitude, after a certain point, doesn’t decrease with distance, and is on the order of 100,000 tons. For a subatomic particle, which usually has a mass on the order of 10^-27 grams, this is obviously a huge force, and this is the reason why we can’t isolate a quark: whenever we try to pull one away from other quarks, the energy we have to put into it to move it away eventually gets so large that a new quark-antiquark pair spontaneously forms and combines with the quarks and gluons to form hadrons, in a process aptly called hadronization. So why don’t the quarks in my body attract me to the quarks in the keyboard that I’m typing on?

It’s because protons and neutrons don’t have ‘color’. Color is a property of particles similar to electric charge in that it determines their interaction with a force (in this case, the strong force). It has nothing to do with actual color; it’s just an unfortunate naming coincidence. A quark is either red, green, or blue, and antiquarks are either antired, antigreen, or antiblue. A particle such as a proton or neutron must have zero net color, and since a proton is three quarks, it is therefore made of a red quark, a green quark, and a blue quark. However, since the strong force constantly shifts colors, there is no one quark that is red; rather, there is always a red, green, and blue quark. Now, red + green + blue = ‘white’, just like with normal color, and colorless particles don’t interact via the strong force. So protons and neutrons aren’t attracted to each other (at least not via the strong force).

However, there is a bit of residual force; this is the nuclear force, or what some people call the ‘strong force’, using ‘color force’ for quark-quark forces. This residual force, however, dies off very quickly due to the mathematics of the strong force. You can’t just add up the individual forces between quarks like you do with electromagnetism.