What is the new color that forms in the image when photographing a sun or similar things (see attachment with a rose glare)?
Why and how it forms?
Is it good for a image?
How to increase or decrease it?
You can get all sorts of interesting shapes and colours when shooting directly into a lightsource like that. All pieces of glass reflect a certain amount of light and transmit a certain amount, so you actually get flare from everything in your scene every time you shoot, only it's usually much dimmer than the rest of the picture so you don't see it.
When you shoot into a lightsource like that, what shows up white (the flame in this case) is actually way way brighter than white, it's just the camera sensor only records up to a certain brightness. So because the object emitting light is very bright, the internal reflections it generates are much brighter and so they show up as flare.
As different colours of light are bent different amounts by the lens optics they are also reflected different amounts so it's not unusual to have strongly coloured flare. Whether it's good or not is up to you, like many things in photography some people will like it and some wont.
You won't eliminate flare when shooting directly into a bright lightsource, but it will change position as you move, also different lenses show different types of flare and to different degrees, so you just have to experiment as it's hard to predict. Filters on the front of the lens can make flare worse as there's an extra glass surface to reflect light.