Child Psychology... Just Cant Deal With It??

Have you considered that he might be color-blind? There are different types of color-blindness, and not being able to tell red and green apart is very common. Does he recognize other colors? You may want to look into this possibility.

I did write a long and boring explanation for this one, but I tried to add HTML code to a few words for dramatic effect and it got deleted. This time I'll give you the short...
...Make sure when teaching colors to use the same item, for example, use two apples, a Granny and a Delicious.
This will eliminate the name of the object coming into question. Don't even say the object name, just the color. Once he has the concept of color, you may now start to teach him the different colors.
My three year old daughter has learned soooooo much from her older sisters (6) that she even knows some colors in two languages (Dora helped her, too). (I don't think she understands that she knows two languages)

Sounds like my oldest!! She had a difficult time tying the colors to the item I was showing her. I found that I had to change the way I was speaking to her.

I started out with a crayon box, and only a few colors.

Red, Blue and Green.

I would point to each item and say, "This is a RED Crayon, This is a BLUE crayon and this is a GREEN crayon."
Then we would go around her room and find things that were the same color as the crayon.

She would point to the item and I would say GOOD JOB that is a RED BALL. Once she got those colors down we went on to others.

This was a process but it did work.

He is only three so try crayons and just say the name of the
color like this is red, or this is blue, and do this
over and over.he will soon pick it up.

Hi nupats. My daughter was also like that when
we started teaching her colors. The tips given by one of the
respondents here MagicGuy would be very helpful. That's how I
taught my daughter. I also used plain colored card boards instead
of pictures to eliminate confusion. Don't worry, your son will learn
in due time. Be patient.

some of the suggestions posted are effective. if i may share, when i was teaching my son about colors, i remember using the book "pat the bunny", picture cards that show colors on one side and common objects associated with that color on the other side. I also supplemented it with colored building blocks. patience is the key.