I've moved this to homework help.
Before we can help you, you need to tell us more about what you want to do. "making a sensor color" seems to indicate you want to make a sensor that can differentiate between colours. Is that right?
Do you just want to be able to differentiate between a red object and a blue object, or differentiate between objects of different shades of blue (for example)?
Can you allow the sensor to be placed on colour to be sensed, or do you want to sense it remotely?
In both cases the former is far easier than the latter.
What resources do you have on hand. If you have nothing, what budget do you have?
And finally, have you considered how you might sense the colour of something? There are many ways and I'm sure you can come up with a few. Maybe if you do, we can suggest some others.
Finally, what is this project for? Is this a high school science project, or a post-graduate project (or somewhere in between)?