Teaching your kids colors can be done a zillion different ways.  But it is usually fun and one of the first things a child picks up, along with animals and shapes.  I hesitate to put an age on any skill, but most two year olds are capable of learning four to ten standard colors—some earlier, some later.

One sign that your child is interested in colors is that he/she calls everything by one color name.  Our last toddler started calling everything “blue.”  But of course he called all adults “Steve” too, so that was probably the influence of his favorite show 😉  Don’t be discouraged if you start teaching your child colors and they do this first, though.  They may go through a stage where everything is “blue” and then everything is suddenly “red.”  Then everything is “green.”  But they will diverge soon enough.

One simple way of teaching colors is to routinely separate something such as Duplo Legos into color piles, and have your child help you.  This teaches categorization as well as discrimination, but usually the child picks up what you are doing before they are verbally able to express it.  You might have all kinds of different shape legos in a pile, but they will pretty naturally catch on that you are separating by color not shape.  At first they might try to “help” you by throwing just any old lego into your pile.  So help them learn by taking it out and saying something (kindly) like, “No, not that one.  We want a GREEN one.  Try this one.”  And then hand them a green one to throw into your pile.  After doing this a couple times, they will probably catch on.  If not, try again later.
Once they have learned to color discriminate the legos (i.e. they can separate into piles by themselves), then start stressing what the color names are.  Tell them to separate their legos into red, yellow, green, and blue piles (or whatever colors you have), and then start naming them and pointing… “This is the GREEN pile.  Green…  This is the BLUE pile.  Blue…”  And then I’d pick just two piles and go back and forth, engaging the child by having them point or pick up a piece… “Green… Blue… Green… Blue.”  Then start dividing the piles up between the two of you, like dealing cards…. “GREEN for you, BLUE for me.  BLUE for you, GREEN for me.”  After you do this a dozen times, depending on how verbal your child is, they might start trying to repeat you.  If not, just test their comprehension by asking them, “OK, now give me one of your BLUE ones.”  And see if they have the idea.  If not, just try again tomorrow.

You can periodically test them later in the day by pointing out things which are blue and green in your own house.  Just make sure to stick with things that are obviously blue and green like their legos, not things that are light or dark shades (that comes later).  Label things that are blue and green, and then ask them what color something is (something that is blue or green).  When they are able to start pointing out blue or green things to you with accuracy, you know they have got it.  Have fun pointing out whichever color they choose first, and then expand to the two.  Your goal is for them to learn at least red, yellow, green, and blue, which they will do probably faster than you think, once the first is mastered.

Some tips:

Don’t try to teach colors by labelling the wrong colors they give you.  Don’t say things like “No, this one’s orange.  You want blue.”  This throws in something they don’t learn/process.  Just say, “No, not that one.  Blue.”  And help them by saying, “This one’s blue.”

Similarly, don’t try to teach too many colors at once unless they are up for it.  Start with two until they are consistently in their vocabulary.

Some lego sets come with light and dark greens or blues.  Throw them out of the mix for awhile and just go with the standard green and blue.

A good color video is “Colors” by Baby Bumblebee.  Buy it wherever you want, but its home site is here: http://www.babybumblebee.com/store/dtls_crzy_color.cfm 

Continue to support color learning even once they seem like they have mastered it.  Like anything else, it drives you crazy for awhile, but it probably takes 6-12 months to completely cement.  Plus, in that bonus time, they can start to distinguish shades and patterns (like “checks” or “polka dots” etc.)

Note: Colorblindness does exist, but even the smartest child is capable of making you think he is colorblind when he really isn’t!  You would have noticed colorblindness if your child couldn’t get past the lego sorting stage.  Or if he could categorize by blue and yellow but not red and green.  (Red/Green colorblindness is probably the most common type, and mostly in males).   Once they are older, it is still common for children to disagree with you on close shades such as pink/red, orange or green/yellow, blue/purple.  This is probably not because they are seeing the color wrong as much as they are cognitively applying the wrong label to the ambiguous shade—most people learn to call magenta “pink” or turquoise “blue” by custom, not by objectivity.