First of all, the black and white markers doesn't reflect the position of the color in the hidden combination (that's your job to figure out). Let's take a look at the example below:

A black marker means that one of the colors in your guess is also in the hidden combination and in the correct slot, so if you have a red color in slot 3 and the hidden combination also has a red color in slot 3 that would result in a black marker in the first correction hole.

A white marker means that one of the colors in your guess is also in the hidden combination BUT in the wrong slot from yours, so if you have a blue color in slot 4 and the hidden combination has the blue color in slot 1 then this would result in a white marker in the second correction hole and so on...

The correction routine always checks for black markers first then white, and the result is shown to the right of your guess from left to right starting with black markers.

If the markers would reflect the positions of the colors then the game would be to easy!

To get more information regarding the rules, just go to your favorite search engine and search for 'Mastermind rules'