The time has come to teach your child colors by sight and you are at a loss of how to accomplish this. There are a few things to keep in mind.
1) Repetition is key. You will have to repeat yourself over and over before they get the hang of it. (Just think of it as practice for your child's teenage years).
2) Your child is probably not color blind. Often times a child will learn the word for a color and really like the sound of the word so when you ask what color something is they will always say "Pink" or "Blue" or "Green". This is not uncommon so do not panic yet.
3) The easiest way to learn this is with every day items.
The first thing I did was get a cheap little photo album that you carry in a handbag. After that I went through the house taking pictures of some of his favorites toys. I chose 5 red toys, 5 blue toys, 5 green toys and 5 yellow toys to start. After those pictures were in the album in order (all the reds, then the blues, the greens and yellows) I found a ball in each color and lined them up side by side and took another picture. I thought of this as our "test page". The idea is to keep this album on you and when you are waiting in the grocery line or the doctor's office or wherever, whip it out and try to teach the colors. When you play with the toys at home, always call them by name and color. For example, if your child wants to play with the Elmo toy, it is the Red Elmo. Like I said, repetition is key.
Once your child has mastered the album, it is time to move onto something a little more difficult. I used an empty coffee can and cut a slit in the lid that was big enough for color pieces to fit through. These pieces are about the size of poker chips. They come in red, blue, green, yellow and orange. Now he has to sort them all out by color and then put them in the slit into the can. This reinforces his learned colors, teaches him a new color and works on his fine motor skills since it takes concentration to get the chips in the slit.
Now it is time to move onto the sorting bears. I am a huge fan of sorting bears as they can be used for so many different things. Teaching colors, teaching patterns, pouring etc. They may come in other colors but ours are red, blue, green, yellow and purple. Notice again that I am only moving onto one more color (purple). Our bears came with the matching cups so we pour out all of the bears and we set the cups at different areas on a table. My son has to get one bear at a time and put it in the appropriate color cup. Once he masters that then we move on to patterns. I will line up different color bears, like blue, yellow, green, red, purple, blue, yellow, green, red & purple. He has to continue the pattern. Since we have also learned orange from the color pieces, I will sometimes throw them into my pattern also.
Now once your child seems to be getting the hang of the 6 colors you taught them, it is time to up the ante a little. Go to the nearest paint department and get some paint samples. I get two of each sheet that I am interested in. When I get home I cut the sheets apart (mine came with three different shade values per card) and make a matching game for him. Once he can effectively match the cards we discuss the colors of each card and how there are light pinks and dark pinks, etc.
I hope this helps you in teaching a child their colors. It is very satisfying when they finally start naming the correct colors.