Color is derived from the perception of different wavelengths of light. Let me explain. Have you ever seen a color wheel? For instance, white light is the addition of all colors of light, where each color has a different wavelength of light. Because of the way that human color perception works, we only need the summation of red, blue, and green lights to see white light. So, to address your questions, what is color, and why do things have different colors, we have to think about how different things interact with white light. We've said that white light contains all different wavelengths of light (its an infinite number of colors). Some materials will absorb or scatter certain wavelengths (colors) while reflecting or transmitting others. So, when you shine white light onto a backpack that looks red, there are dyes in the fabric of the backpack which are absorbing the green and blue components of the light, and only the red component of the light makes it to your eye, allowing you to see a red backpack. Excellent question and difficult to answer!

Great question!
Its a complex topic but I will try my best. So, things that have color consist of different materials, which consist of different chemicals, which consist of different atoms. All these elements are responsible for the properties of the surface of the thing that reflects light. The way the thing reflect light we see as color.

Think of atoms like little bricks and chemicals like the way the wall is made from those bricks. So now you throw the ball into the wall. Depending of whether the wall is smooth or has sharp corners, or bended, or has big holes or has holes where the ball may stuck, your ball may jump back in different directions or just go through the wall, or be stuck in one of the tricky corners. Same with every surface when light hits it, surface may reflect the light back; it can absorb light or just let it go through (transparent things).

So now, we need to talk more about light: we were talking about one ball hitting the wall, while light is more like a lot of balls of different size hitting the wall at the same time. Because balls are of different size, some of them will be mostly bounded back, while others may be mostly stuck in the wall. Different objects (like lamps or sun or fire) emit energy (we imagine it as "balls" for now). Those balls are of different size. If you collect them from all over the universe and put all in the order from the very little to the very big you get what scientists call "spectrum" - the range of energy from ultraviolet to radio waves. Our sun emits energy of certain range (balls sizes are, lets say, only from 2 to 5 cm, not more, not less). So our eyes were developed to be sensitive only to those size of "balls" (others were not important as there were not many hitting our earth). so when sunlight hits the surface, for example the plant leave, the balls size 4 are mostly jumping back (while others are absorbed), and balls 4 reach our eyes. Our eyes react to the "balls" of certain size as color. So ball size 4 we call "green", the balls size 2 we call blue etc.

So now, the interesting conclusions: things do not have color by themselves. only when light (energy) hits them - we can see colors. You probably noticed that when it is dark, things get grayish and its hard to distinguish colors. Another interesting conclusion - our eyes are only sensitive to a little part of spectrum, or in other words can see only a little part of all possible colors. Thats why we develop instruments, like different spectrometers to learn about those "balls" we can not see with our eyes.

And, finally, summing up the story: colors are out interpretation on the ability of things (surfaces) to reflect the certain part of light. And different things have different colors as their light reflecting properties are different.

Color comes from the frequency of light that our eyes respond to. Objects either reflect or glow in the color that we see them, and absorb other colors (or glow more strongly in one color than in another).

This a is good question. As with many things in the physical world, we construct our reality from the world. What I mean is that "color" is not something that is OBJECTIVELY in the world. Rather, color is subjective. For example, the reason you see something as red is because the light that reflects on your retina is a certain frequency that is visible to your retina. There is also a dedicated region in your brain (called V4, in the visual occipital cortex) that determines the color you see. When certain unfortunate people have injuries to their brains, they have a rare abnormality called achromatopsia where they don't perceive color anymore as they used to prior to the brain trauma. There is also an interesting phenomenon called synesthesia where people experience tastes when they see certain colors or vice versa--colors when they taste certain foods. All this is evidence that we, through our sensory organs and our brains, construct our subjective reality. I suggest you watch the film Matrix and think about this.

Color is actually specific energies of light waves which fall into the range of visible spectrum ranges between red and violet. We see objects as a specific color because of the color effect. For example when a blue object is hit with light rays the object reflects only blue light and absorbs all other light. The why is a little harder to answer. I can offer an answer as it pertains to plants. Plants are green because they contain a cell called chloroplasts which uses all wavelength of light except for green to perform photosynthesis. So we primarily see plants as green because green is the most color predominately reflected.