Try to reach all 5 senses if you can. For sight, put different colored objects around the room for the students to find the yellow, blue, green, etc. objects. Yes, flashcards are good = holding up the colors and they could call out the color, or stand up for a certain color, raise hand, even write it down. In learning another language, it is helpful to reach all types of learning.
1. sight = they need to SEE what is to be learned.
2. auditory = they need to HEAR what is to be learned.
3. kinesthetic = they need to be PHYSICALLY involved = tracing, walking through, etc.
4. many people are a combination of 2 of the 3 types of learning.
I had an entire file cabinet full of: activities, people, scenes, etc. from old magazines, laminated on colored paper. That way you could ask "who has the green sweater" etc. Don't be afraid to be imaginative, depending upon the age group.
If you would like any ESL sites, etc. I have many. Even old drawing books and with crayons, you could tell them what color to make certain objects.
P.S. Here is a GOOGLE Search with ideas: