Sigit, from somebody here in CA, I got link to this, somewhere there is blending tutorial. Sorry, it's not much but if you browse few pages back, you will surely get good answer for your question, because people are asking about blending all the time.
panda I'm only using the photo as a background so the shape is the same. I'm coloring it by using eyedropper and brush.
I'm sorry if thats not allowed. I'll try to make a new one
But you're here to learn, right? Part of painting is being able to eye an object and then select appropriate colours to render it. If all you're doing is picking colours off the original photo, and then putting them directly over the top of the photo, then what are you learning?
The answer is nothing.
No one here is going to make fun of you if your apple has a different shape to the original photo, or if the colours you picked aren't exactly the same as the ones in the photo. Explore the object in your own way, and do the best with what you know, then post what you can do here and people will help you improve and learn.
Never be afraid to use crutches, they are there to help you learn to walk. Be afraid of dependence upon crutches, for you will never run.
Color picking can be a useful crutch. Use it if you must in order to focus on other elements, use it to help you learn color as well. But please - experiment as much as possible with tools, techniques and process.
Color picking, in my opinion, is best saved for use later in the images developement. Start by laying in all of the basic color transitions yourself. What you are learning here is observation. When you understand what you are seeing you are making a huge leap in your ability paint. It's best to look, choose a color yourself that you think comes close to what you see, try it and see how it relates to the other colors you put down. That is a key part of the learning process which you'll miss by picking a color directly.
Later, once you have everything down correctly and you are smoothing out color transitions and making the form look correct, at that point use the color picker, but pick from within your own image as needed. You've already made your color decisions at that point, and the color picker can be used as a slight shortcut, or to make sure you stay consistant.