The subject of colour can become very complex with lots of mathematics and physics involved.
That is way beyond the scope of this article.
With Photoshop™, or other post processing software, colours can be changed subtly or dramatically depending on what you want the final image to look like.
When you first start the tendency is to change all of the colours using hue/saturation and vibrancy. You then progress to selectively changing the colour of just one object or part of the scene at a time.
So what are we trying to achieve. Leaving aside the more surreal and abstract productions we are trying to reproduce a vision which is eye catching and appealing.
This is where colour is so important. It is rare that you can ever achieve absolute perfection because each person perceives colour differently. Some prefer blue, some red and so on. You may also want to change the colour balance to affect the mood conveyed. A warm looking cosy scene compared to a cold sharp one.
Experimentation and looking at other photographers work will help to achieve what you desire.
There is one important consideration, however, that applies to all photos.
Lets start with a bit of theory:
When you look at an object or scene what you see is the light reflecting from that object.
Colour vision is a process by which either you, or a camera, are able to recognize that object based on the different wavelengths of light reflected by that object.
The eye sends the information it receives to the brain which which in turn processes those sensations into a subjective perception of color. With a digital camera it processes the information the sensor has received but unlike the human brain it records it just as it has seen it with no subjective adjustment.
Color constancy is a process that allows the brain to recognize a familiar object as being a consistent color regardless of the amount of light reflecting from it at a given moment.
The intensity of light, how bright it is and what type of light, affects the final image with a camera but the brain makes adjustments for this.
Put simply if you have a white boat on a bright blue sea the blueness will be reflected onto the boat making it look blue. The camera will interpret this literally but the eye still perceives it as a white boat and has therefore made an adjustment. It preserves the appearance of an object under a wide range of light sources
A camera also has a more limited ability to capture different tones than the eye. This is where HDR photography tries to compensate for this. Through the fusing of a number of different exposures it it is trying to capture the same tones and colours as the human eye. This is why a good photorealistic (as opposed to a cartoony style) hdr photograph appears to bring the scene to life.
Now a practical example:
Here is the normal exposure straight from the camera. Notice the ‘flatness’ of the image and very blue. The shadows look dark because the camera is pointing virtually straight into the sun and the camera is trying to compensate for the brightness.

Normal exposure
Now an hdr version. This has brought out the detail and compensated for the dark shadows but is still very blue. You cannot blame the camera or the hdr software because it was a very blue scene and everything was reflecting blue.

hdr version
Now a colour compensated version. This is more like the eye is expecting and is more visually comfortable. The eye does not have to compensate so much and appreciates that.

color corrected
I hope, by now, that you will realise the importance of post processing and getting the colours as appealing as you can.
Happy photographing.
Steve