like invisible :) or like this

If you could see them? Because they are pretty small....Umm.....Like little yellow spheres...or something like that.....Hmmmm Good question

You cannot really see electrons, since they are much smaller than the wavelength of light. They are literally too small to see.

Look in your hand, because you have a handfull of electrons there already. Since the electrons in your example would all be uncoupled and negatively charged, you would probably see a large spark, similar to static electric discharge. But the real question is, what does an electron look like. And the answer, unfortunately, is that we can never know. To fully understand you would need to read a book on quantum mechanics. Basically, when we talk about "seeing" something, what we mean is that we bounce a large number of light rays off of it and register the results with the nerve ending in our eyeballs. You really can't bounce light rays off of an electron. They would knock it out of position and you would never get a coherent picture in your eye. In the old days of Newtonian physics, it was considered that electrons were like tiny charged billiard balls. It is important to realize that this was just a conceptual model and not reality. In this post-modern age of quantum mechanics it is best to think of electrons as ideas that explain observations, or pools of delayed time in the time-space continuum, rather than physical objects that we can see the same way we can see a lifesized object.

The closest you come in real life is a good conductor/metal: these are lots of freely movable electrons around the (more or less) static atoms. (the basic theory for this is the so-called Drude model, which is also valid for cold dense plasmas, see http://en.wikipedia.org/wiki/Drude_model). So it could look very shiny and reflecting, if the density of the electrons is high enough (like 10^20 electrons per ccm; if the density is much lower, light would just pass through).